Главная Software Testing: An ISTQB-BCS Certified Tester Foundation Guide 3rd ed
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SOFTWARE TESTING BCS, THE CHARTERED INSTITUTE FOR IT BCS, The Chartered Institute for IT champions the global IT profession and the interests of individuals engaged in that profession for the benefit of all. We promote wider social and economic progress through the advancement of information technology, science and practice. We bring together industry, academics, practitioners and government to share knowledge, promote new thinking, inform the design of new curricula, shape public policy and inform the public. Our vision is to be a world-class organisation for IT. Our 70,000 strong membership includes practitioners, businesses, academics and students in the UK and internationally. We deliver a range of professional development tools for practitioners and employees. A leading IT qualification body, we offer a range of widely recognised qualifications. Further Information BCS, The Chartered Institute for IT, First Floor, Block D, North Star House, North Star Avenue, Swindon, SN2 1FA, United Kingdom. T +44 (0) 1793 417 424 F +44 (0) 1793 417 444 www.bcs.org/contact http://shop.bcs.org/ SOFTWARE TESTING An ISTQB–BCS Certified Tester Foundation guide Third edition Brian Hambling (editor), Peter Morgan, Angelina Samaroo, Geoff Thompson and Peter Williams © 2015 BCS Learning & Development Ltd The right of Brian Hambling, Peter Morgan, Angelina Samaroo, Geoff Thompson and Peter Williams to be identified as authors of this work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. All rights reserved. Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted by the Copyright Designs and Patents Act 1988, no part of this publication may be reproduced, stored or transmitted in any form or by any means, except with the prior permission in writing of the publisher, or in the case of reprographic reproduction, in accordance with the terms of the licences issued by the Copyright Licensing Agency. En; quiries for permission to reproduce material outside those terms should be directed to the publisher. All trade marks, registered names etc. acknowledged in this publication are the property of their respective owners. BCS and the BCS logo are the registered trade marks of the British Computer Society charity number 292786 (BCS). Published by BCS Learning & Development Ltd, a wholly owned subsidiary of BCS, The Chartered Institute for IT, First Floor, Block D, North Star House, North Star Avenue, Swindon, SN2 1FA, UK. www.bcs.org Paperback ISBN: 978-1-78017-299-6 PDF ISBN: 978-1-78017-300-9 ePUB ISBN: 978-1-78017-301-6 Kindle ISBN: 978-1-78017-302-3 British Cataloguing in Publication Data. A CIP catalogue record for this book is available at the British Library. Disclaimer: The views expressed in this book are of the author(s) and do not necessarily reflect the views of the Institute or BCS Learning & Development Ltd except where explicitly stated as such. Although every care has been taken by the author(s) and BCS Learning & Development Ltd in the preparation of the publication, no warranty is given by the author(s) or BCS Learning & Development Ltd as publisher as to the accuracy or completeness of the information contained within it and neither the author(s) nor BCS Learning & Development Ltd shall be responsible or liable for any loss or damage whatsoever arising by virtue of such information or any instructions or advice contained within this publication or by any of the aforementioned. BCS books are available at special quantity discounts to use as premiums and sale promotions, or for use in corporate training programmes. Please visit our Contact us page at www.bcs.org/contact Typeset by Lapiz Digital Services, Chennai, India. iv CONTENTS Figures and tables Authors Abbreviations Preface INTRODUCTION Nature and purpose of the book Purpose of Foundation The Certified Tester Foundation Level syllabus Relationship of the book to the syllabus How to get the best out of this book vii ix xi xii 1 1 1 2 4 4 1. THE FUNDAMENTALS OF TESTING Background Introduction Why software fails Keeping software under control What testing is and what testing does General testing principles Fundamental test process The psychology of testing Code of ethics Summary 6 6 6 8 11 14 15 20 26 27 28 2. LIFE CYCLES Introduction Software development models Test levels Test types Maintenance testing Summary 37 37 39 45 52 54 55 3. STATIC TESTING Introduction Background to static techniques Reviews and the test process Static analysis by tools Summary 60 60 62 62 71 73 v CONTENTS 4. TEST DESIGN TECHNIQUES Introduction The test development process The idea of test coverage Categories of test case design techniques Specification-based (black-box) techniques Structure-based (white-box) techniques Experience-based techniques Choosing test techniques Summary 77 77 79 83 84 85 100 126 128 129 5. TEST MANAGEMENT Introduction Risk and testing Test organisation Test approaches (test strategies) Test planning and estimation Test progress monitoring and control Incident management Configuration management Summary 139 139 142 145 150 152 159 165 168 169 6. TOOL SUPPORT FOR TESTING Introduction What is a test tool? Test tools Introducing a tool into an organisation Summary 175 175 177 181 212 216 7. THE EXAMINATION The examination Revision techniques Review 223 223 227 228 APPENDICES A1 Mock CTFL examination A2 Mock CTFL examination answers A3 Mock CTFL examination commentary 229 231 245 246 vi Index 259 FIGURES AND TABLES Figure 1.1 Effect of an error Figure 1.2 Resources triangle Figure 1.3 Effect of identification time on cost of errors Figure 1.4 Fundamental test process Figure 1.5 Iteration of activities Figure 2.1 Waterfall model Figure 2.2 V-model for software development Figure 2.3 Iterative development Figure 2.4 Top-down control structure Figure 2.5 Bottom-up integration Figure 3.1 Stages of a formal review Figure 3.2 Formality of reviews Figure 4.1 State transition diagram of the hill-walker’s watch Figure 4.2 State transition diagram Figure 4.3 Use case example Figure 4.4 Flow chart for a sequential program Figure 4.5 Flow chart for a selection (decision) structure Figure 4.6 Flow chart for an iteration (loop) structure Figure 4.7 Flow chart representation for Example 4.5 Figure 4.8 Control flow graph showing subgraphs as nodes Figure 4.9 Control flow graph with subgraphs expanded Figure 4.10 Flow chart for Coverage example Figure 4.11 The hybrid flow graph Figure 4.12 Paths through the hybrid flow graph Figure 4.13 Paths through the hybrid flow graph Figure 4.14 Paths through the hybrid flow graph Figure 4.15 Simplified control flow graph: a decision Figure 4.16 Simplified control flow graph: locations of a decision in a loop Figure 4.17 Example of how simplified control flow graphs are read and interpreted Figure 4.18 Control flow graph for Exercise 4.11 Figure 4.19 Test case for examination question E4 Figure 4.20 Test case for examination question E5 Figure 4.21 Flow chart for Exercise 4.6 Figure 4.22 Control flow graph for Exercise 4.6 Figure 5.1 Levels of independent testing Figure 5.2 Test plans in the V-model Figure 5.3 iTesting Executive Dashboard 10 12 18 20 21 39 41 43 47 48 65 68 96 98 99 104 104 104 106 109 109 112 112 113 115 119 121 122 123 125 131 132 135 136 146 153 161 vii FIGURES AND TABLES Figure 5.4 Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure A1.1 Figure A1.2 Figure A1.3 Figure A1.4 Incidents planned/raised Test tool payback model Hotel system architecture An integrated set of tools Test execution tools payback model Test harness for middleware Test tool implementation process State transition diagram for question 8 State transition diagram for question 9 Control flow diagram for question 18 Flow graph for question 19 162 178 180 182 196 197 217 233 234 237 238 Table 1.1 Table 4.1 Table 5.1 Table 5.2 Table 5.3 Table 5.4 Table 6.1 Table 6.2 Table 6.3 Table 6.4 Table 6.5 Table A1.1 Comparative cost to correct errors ST for the hill-walker’s watch Features of independent testing Test plan sections Test summary report outline Test incident report outline Configuration traceability Hotel system extract (20/10/2014) Hotel system extract (5/11/2014) Exit criteria Types of test tool State transition table for question 9 17 97 147 154 163 167 186 192 193 199 207 234 viii AUTHORS Brian Hambling has experienced software development from a developer’s, project manager’s and quality manager’s perspective in a career spanning over 35 years. He has worked in areas as diverse as real-time avionics, legacy systems maintenance and ebusiness strategies. He contributed to the development of software quality standards while at the Ministry of Defence and later became the head of systems and software engineering at The University of Greenwich. He was technical director of ImagoQA and general manager of Microgen IQA, a specialist company providing consultancy in software testing and quality assurance primarily to the financial services sector. He is now concentrating on writing. Peter Morgan was a freelance testing practitioner, now mainly retired. He worked as a hands-on tester for a number of years, often on large projects. He has worked in many business sectors in the UK, and has been involved with the examination side of testing since taking the Foundation Certificate in 2001. Peter still writes exam questions and regularly reviews course submissions of testing courses on behalf of the UKTB, looking for syllabus compliance and to see that potential students are well prepared for their own exams. Angelina Samaroo has a degree in Aeronautical Engineering from Queen Mary University of London. She is a Chartered Engineer and Fellow of the Institution of Engineering and Technology (IET). She spent 10 years working on the mission software for the Tornado ADV fighter jet. During this time she took an interest in the career development of new engineers and led the company graduate development scheme. She then joined a small consultancy in software testing, specialising in providing training to test professionals worldwide. She now works for Pinta Education Limited and provides training in software testing, business analysis and programming. Geoff Thompson is the Consultancy Director for Experimentus Ltd, a leading software quality management consultancy based in the UK. He has a real passion for quality and software testing and over the last 25 years has an excellent track record in test management and process improvement. In 1997, he started working with BCS/ISEB developing the original Software Testing Foundation syllabus and exams; he then managed the development of the original Software Testing Practitioner syllabus and exam in 2002. Geoff initiated the International Software Testing Qualification Board (ISTQB) and is its UK representative. He chairs the UK Testing Board. ix AUTHORS He is a founding member of the TMMi Foundation and chairman of the TMMi Foundation management executive (see www.tmmifoundation.org.uk) He is also the vice-chairman and treasurer of the BCS specialist group in software testing (SIGiST). In 2008, Geoff was awarded the European Testing Excellence Award. He is a popular speaker, and has recently delivered keynote presentations in India and Australia, as well as being a regular speaker at EuroSTAR, for which he was the programme chair in 2011. Peter Williams previously worked in methods and systems improvement before moving into systems development and subsequently software testing. He has been a self-employed contract test manager or consultant in both financial services and the public sector. He has evaluated test processes and subsequently implemented improvements, at various organisations, including test management and execution tools as appropriate. He has an MSc in computing from the Open University and was chairman of the Examinations Panel for the ISEB Foundation Certificate in Software Testing. x ABBREVIATIONS AUT BACS CFG CMMI COTS CTFL DOS DSDM FTP GUI ISEB ISTQB MISRA RAD RUP SDLC SIGiST SQL ST TPI UML XML Application Under Test Bankers Automated Clearing Services Control Flow Graph Capability Maturity Model Integration Commercial Off-The-Shelf Certified Tester Foundation Level Denial of Service Dynamic Systems Development Methodology Fundamental Test Process Graphical User Interface Information Systems Examination Board International Software Testing Qualifications Board Motor Industry Software Reliability Association Rapid Application Development Rational Unified Process Software Development Life Cycle Specialist Interest Group in Software Testing Structured Query Language State Table Test Process Improvement Unified Modeling Language Extensible Markup Language xi PREFACE When I started work on the first edition of this book in 2006, I little thought that I would be drafting a preface to a third edition in 2015. My fellow authors and I have been amazed at the continuing success of this simple guide to understanding the ISTQB Foundation Certificate in Software Testing and passing the exam, yet feedback from readers who have passed the exam by using this book as their sole preparation has been steadily amassing. In this third edition, we have tried to provide some new material and even better exam preparation resources. Many of the exercises, examples and sample questions have been updated to reflect the way the exam has evolved over the years, and for this edition we have put together a complete mock examination. This gives commentary to explain the correct answer and why each of the distracters is incorrect. Moreover, as a mock exam, the candidates can time themselves to check they are prepared for the real thing. We think that this is a major improvement on previous editions and we hope you will find it really useful. xii INTRODUCTION NATURE AND PURPOSE OF THE BOOK The Foundation Certificate in Software Testing was introduced as part of the BCS Professional Certification portfolio (formerly ISEB) in 1998; since then over 300,000 Foundation Certificates have been awarded. An intermediate level certificate was introduced in 2007 as a step towards the more advanced Practitioner certificates. (Visit www.bcs.org/certifications for more information.) The International Software Testing Qualifications Board (ISTQB) (www.istqb.org) was set up in 2001 to offer a similar certification scheme to as many countries as wished to join this international testing community. The UK was a founding member of ISTQB and, in 2005, adopted the ISTQB Foundation Certificate syllabus as the basis of examinations for the Foundation Certificate in the UK. The Foundation Certificate is now an entry qualification for the ISTQB Advanced Certificate. The Certified Tester Foundation Level (CTFL) syllabus has been updated and released in a 2010 version, and this book relates to the 2010 version of the syllabus. This book has been written specifically to help potential candidates for the ISTQB–BCS CTFL examination. The book is therefore structured to support learning of the key ideas in the syllabus quickly and efficiently for those who do not plan to attend a course, and to support structured revision for anyone preparing for the exam. In this introductory chapter we will explain the nature and purpose of the Foundation Level and provide an insight into the way the syllabus is structured and the way the book is structured to support learning in the various syllabus areas. Finally we offer guidance on the best way to use this book, either as a learning resource or as a revision resource. PURPOSE OF FOUNDATION The CTFL Certificate is the first level of a hierarchy of ISTQB–BCS certificates in software testing, and leads naturally into the next level, known as the Intermediate Certificate in Software Testing, which in turn leads on to the ISTQB Advanced Level, followed by the various ISTQB Expert Level examinations. The Foundation Level provides a very broad introduction to the whole discipline of software testing. As a result coverage of topics is variable, with some only briefly mentioned and others studied in some detail. The arrangement of the syllabus and the required levels of understanding are explained in the next section. 1 SOFTWARE TESTING The authors of the syllabus have aimed it at people with various levels of experience in testing, including those with no experience at all. This makes the certificate accessible to those who are or who aim to be specialist testers, but also to those who require a more general understanding of testing, such as project managers and software development managers. One specific aim of this qualification is to prepare certificate holders for the next level of certification, but the Foundation Level has sufficient breadth and depth of coverage to stand alone. THE CERTIFIED TESTER FOUNDATION LEVEL SYLLABUS Syllabus content and structure The syllabus is broken down into six main sections, each of which has associated with it a minimum contact time that must be included within any accredited training course: 1. 2. 3. 4. 5. 6. Fundamentals of testing (155 minutes). Testing throughout the software life cycle (115 minutes). Static techniques (60 minutes). Test design techniques (285 minutes). Test management (170 minutes). Tool support for testing (80 minutes). The relative timings are a reliable guide to the amount of time that should be spent studying each section of the syllabus. Each section of the syllabus also includes a list of learning objectives that provides candidates with a guide to what they should know when they have completed their study of a section and a guide to what can be expected to be asked in an examination. The learning objectives can be used to check that learning or revision is adequate for each topic. In the book, which is structured around the syllabus sections, we have presented the learning objectives for each section at the beginning of the relevant chapter, and the summary at the end of each chapter confirms how those learning objectives have been addressed. Finally, each topic in the syllabus has associated with it a level of understanding, represented by the legend K1, K2, K3 or K4: yy Level of understanding K1 is associated with recall, so that a topic labelled K1 contains information that a candidate should be able to remember but not necessarily use or explain. yy Level of understanding K2 is associated with the ability to explain a topic or to classify information or make comparisons. yy Level of understanding K3 is associated with the ability to apply a topic in a practical setting. yy Level of understanding K4 is associated with the ability to analyse a situation or a set of information to determine what action to take. 2 INTRODUCTION The level of understanding influences the level and type of questions that can be expected to be asked about that topic in the examination. More detail about the question style and about the examination is given in Chapter 7. Example questions, written to the level and in the formats used in the examination, are included within each chapter to provide generous examination practice. Syllabus updates and changes The syllabus was last updated in 2011 and the book is in line with the changes and additions introduced in that version of the syllabus. Since then an extension to the Foundation syllabus has been introduced to cover a significant aspect of software testing that has grown in prominence in recent years. The Foundation Level Extension – Agile Tester is a complete new syllabus with its own separate examination and that syllabus is not addressed in this book. Throughout this book you will find references to different testing standards that form reference points for parts of the ISTQB Software Testing Foundation syllabus. In 2013, ISO replaced the following standards with ISO/IEC/IEEE 29119 Software Testing: yy IEEE 829 Test documentation yy IEEE 1008 Unit testing yy BS 7925-1 Vocabulary of terms in software testing yy BS 7925-2 Software component testing standard At the time of going to press, ISTQB were reviewing the new standard to understand which elements need to be included within all of its syllabuses, so we have not included any detailed references within this book. However, because this is the first international testing standard to cover all elements of the test discipline, it is important that the reader is aware of its existence and, at a high level, what it covers. ISO/IEC/IEEE 29119 Software testing is an internationally agreed set of standards for software testing that can be used within any software development life cycle or organisation. There are currently five standards within ISO/IEC/IEEE 29119: yy ISO/IEC 29119-1: Concepts & definitions (published September 2013) facilitates understanding and use of all other standards and the vocabulary used within the 29119 series. yy ISO/IEC 29119-2: Test processes (published September 2013) defines a generic process model for software testing that can be used within any software development life cycle. yy ISO/IEC 29119-3: Test documentation (published September 2013) defines templates for test documentation that cover the entire software testing life cycle. yy ISO/IEC 29119-4: Test techniques (anticipating publication in 2015) defines software test design techniques (also known as test case design techniques or test methods). yy ISO/IEC 29119-5: Keyword driven testing (anticipating publication in 2015) defines an international standard for supporting keyword-driven testing. 3 SOFTWARE TESTING yy ISO/IEC 33063 Process assessment model (anticipated publication date not known) is an additional standard being worked on alongside ISO/IEC/IEEE 29119. The purpose of 33063 is to define a process assessment model for software testing for use in performing a conformant assessment in accordance with the requirements of ISO/IEC 33002 (Process assessment – Requirements for performing process assessments). RELATIONSHIP OF THE BOOK TO THE SYLLABUS The book is structured into chapters that mirror the sections of the syllabus so that you can work your way through the whole syllabus or select topics that are of particular interest or concern. The structure enables you to go straight to the place you need, with confidence either that what you need to know will be covered there and nowhere else, or that relevant cross references will be provided. Each chapter of the book incorporates the learning objectives from the syllabus and identifies the required level of understanding for each topic. Each chapter also includes examples of typical examination questions to enable you to assess your current knowledge of a topic before you read the chapter, and further questions at the end of each chapter to provide practice in answering typical examination questions. Topics requiring K3 level of understanding are presented with worked examples as a model for the level of application expected from real examination questions. Answers are provided for all questions, and the rationale for the correct answer is discussed for all practice questions. A final chapter explains the Foundation Level examination strategy and provides guidance on how to prepare for the examination and how to manage the examination experience to maximise your own performance. HOW TO GET THE BEST OUT OF THIS BOOK This book is designed for use by different groups of people. If you are using the book as an alternative to attending an accredited course you will probably find the first method of using the book described below to be of greatest value. If you are using the book as a revision aid you may find the second approach more appropriate. In either case you would be well advised to acquire a copy of the syllabus (available from www.istqb.org) and a copy of the sample examination paper (available from BCS) as reference documents, though neither is essential and the book stands alone as a learning and revision aid. Using the book as a learning aid For those of you using the book as an alternative to attending an accredited course the first step is to familiarise yourself with the syllabus structure and content by skim reading the opening sections of each chapter where the learning objectives are identified for each topic. You may then find it helpful to turn to Chapter 7 and become familiar with the structure of the examination and the types and levels of questions that you can expect in the examination. From here you can then work through each of the six main 4 INTRODUCTION chapters in any sequence before returning to Chapter 7 to remind yourself of the main elements of the examination. For each chapter begin by attempting the self-assessment questions at the beginning to get initial confirmation of your level of confidence in the topics covered by that chapter. This may help you to prioritise how you spend your time. Work first through the chapters where your knowledge is weakest, attempting all the exercises and following through all the worked examples. Read carefully through the chapters where your knowledge is less weak but still not good enough to pass the exam. You can be more selective with exercises and examples here, but make sure you attempt the practice questions at the end of the chapters. For the areas where you feel strong you can use the chapter for revision, but remember to attempt the practice questions to confirm positively your initial assessment of your level of knowledge. Each chapter contains a summary section that reiterates the learning objectives, so reading the first and last sections of a chapter will help you to understand how your current level of knowledge relates to the level required to pass the examination. The best confirmation of this is to attempt questions at the appropriate K level for each topic; these are provided in the book. Using the book as a revision aid If you are using this book for final revision, perhaps after completing an accredited course, you might like to begin by using a selection of the example questions at the end of each chapter as a ‘mock examination’. Appendix A1 contains a complete mock exam, with all the answers in Appendix A2, which will provide some experience of answering typical questions under the same time pressures that you will experience in the real examination, and this will provide you with a fairly reliable guide to your current state of readiness to take the real examination. You can also discover which areas most need revision from your performance in the mock exam, and this will guide you as you plan your revision. There is a complete question-by-question commentary on the mock exam in Appendix A3 so that you can identify why you got any questions wrong. Revise first where you feel weakest. You can use the opening sections of each chapter, containing the learning objectives and the self-assessment questions, together with the summary at the end of each chapter to refine further your awareness of your own weaknesses. From here you can target your studies very accurately. Remember that every K3 or K4 topic will have at least one worked example and some exercises to help you build your confidence before tackling questions at the level set in the real examination. You can get final confirmation of your readiness to sit the real examination by taking the sample examination paper available from BCS. 5 1 THE FUNDAMENTALS OF TESTING Peter Morgan BACKGROUND If you were buying a new car, you would not expect to take delivery from the showroom with a scratch down the side of the vehicle. The car should have five wheels, a steering wheel, an engine and all the other essential components, and it should come with appropriate documentation, with all pre-sales checks completed and passed satisfactorily. The car you receive should be the car described in the sales literature; it should have the correct engine size, the correct colour scheme, and whatever extras you have ordered, and performance in areas such as fuel consumption and maximum speed should match published figures. In short, a level of expectation is set by brochures, by your experience of sitting in the driving seat, and probably by a test drive. If your expectations are not met you will feel justifiably aggrieved. This kind of expectation seems not to apply to new software installations; examples of software being delivered not working as expected, or not working at all, are common. Why is this? There is no single cause that can be rectified to solve the problem, but one important contributing factor is the inadequacy of the testing to which software applications are exposed. Software testing is neither complex nor difficult to implement, yet it is a discipline that is seldom applied with anything approaching the necessary rigour to provide confidence in delivered software. Software testing is costly in human effort or in the technology that can multiply the effect of human effort, yet is seldom implemented at a level that will provide any assurance that software will operate effectively, efficiently or even correctly. This book explores the fundamentals of this important but neglected discipline to provide a basis on which a practical and cost-effective software testing regime can be constructed. INTRODUCTION In this opening chapter we have three very important objectives to achieve. First, we will introduce you to the fundamental ideas that underpin the discipline of software testing, and this will involve the use and explanation of some new terminology. Secondly, we will establish the structure that we have used throughout the book to help you to use 6 THE FUNDAMENTALS OF TESTING the book as a learning and revision aid. Thirdly, we will use this chapter to point forward to the content of later chapters. The key ideas of software testing are applicable irrespective of the software involved and any particular development methodology (waterfall, Agile etc.). Software development methodologies are discussed in detail in Chapter 2. We begin by defining what we expect you to get from reading this chapter. The learning objectives below are based on those defined in the Software Foundation Certificate syllabus, so you need to ensure that you have achieved all of these objectives before attempting the examination. Learning objectives The learning objectives for this chapter are listed below. You can confirm that you have achieved these by using the self-assessment questions at the start of the chapter, the ‘Check of understanding’ boxes distributed throughout the text, and the example examination questions provided at the end of the chapter. The chapter summary will remind you of the key ideas. The sections are allocated a K number to represent the level of understanding required for that section; where an individual topic has a lower K number than the section as a whole, this is indicated for that topic; for an explanation of the K numbers see the Introduction. Why is testing necessary? (K2) yy Describe, with examples, the way in which a defect in software can cause harm to a person, to the environment or to a company. yy Distinguish between the root cause of a defect and its effects. yy Give reasons why testing is necessary by giving examples. yy Describe why testing is part of quality assurance and give examples of how testing contributes to higher quality. yy Recall the terms error, defect, fault, failure and the corresponding terms mistake and bug, using examples. What is testing? (K2) yy Recall the common objectives of testing. (K1) yy Provide examples for the objectives of testing in different phases of the software life cycle. yy Differentiate testing from debugging. General testing principles (K2) yy Explain the seven principles in testing. 7 SOFTWARE TESTING Fundamental test process (K1) yy Recall the five fundamental test activities and respective tasks from planning to closure. The psychology of testing (K2) yy Recall the psychological factors that influence the success of testing. (K1) yy Contrast the mindset of a tester and of a developer. Self-assessment questions The following questions have been designed to enable you to check your current level of understanding for the topics in this chapter. The answers are given at the end of the chapter. Question SA1 (K1) A non-functional requirement concerning performance is missing from the system documentation. How should this be described? a. b. c. d. It is a mistake. It is a failure. It is a fault. It is an error. Question SA2 (K1) Which of the following gives MOST independence in testing? a. b. c. d. Testing performed by the person who wrote the code. Testing performed by an external consultancy. Testing performed by another member of the same Agile team. Testing performed by a separate department. Question SA3 (K1) Running the same set of tests will not continue to find new defects. Which of the seven testing principles does this illustrate? a. b. c. d. efect clustering. D Testing shows the presence of bugs. Absence of errors fallacy. The pesticide paradox. WHY SOFTWARE FAILS Examples of software failure are depressingly common. Here are some you may recognise: 8 THE FUNDAMENTALS OF TESTING yy After successful test flights and air worthiness accreditation, problems arose in the manufacture of the Airbus A380 aircraft. Assembly of the large subparts into the completed aircraft revealed enormous cabling and wiring problems. The wiring of large subparts could not be joined together. It has been estimated that the direct or indirect costs of rectification was $6.1 billion. (Note: this problem was quickly fixed and the aircraft entered into service within 18 months of the cabling difficulties being identified.) yy When the UK Government introduced online filing of tax returns, a user could sometimes see the amount that a previous user earned. This was regardless of the physical location of the two applicants. yy In November 2005, information on the UK’s top 10 wanted criminals was displayed on a website. The publication of this information was described in newspapers and on morning radio and television and, as a result, many people attempted to access the site. The performance of the website proved inadequate under this load and the website had to be taken offline. The publicity created performance peaks beyond the capacity of the website. yy A new smartphone mapping application (app) was introduced in September 2012. Among many other problems, a museum was incorrectly located in the middle of a river, and Sweden’s second city, Gothenburg, seemed to have disappeared from at least one map. yy A small, one-line, change in the billing system of an electrical provider blacked out the whole of a major US city. What is it about these examples that make them so startling? Is it a sense that something fairly obvious was missed? Is it the feeling that, expensive and important as they were, the systems were allowed to enter service before they were ready? Do you think these systems were adequately tested? Obviously they were not, but in this book we want to explore why this was the case and why these kinds of failure continue to plague us. To understand what is going on we need to start at the beginning, with the people who design systems. Do they make mistakes? Of course they do. People make mistakes because they are fallible, but there are also many pressures that make mistakes more likely. Pressures such as deadlines, complexity of systems and organisations, and changing technology all bear down on designers of systems and increase the likelihood of errors in specifications, in designs and in software code. These errors are where major system failures usually begin. If a document with an error in it is used to specify a component the component will be faulty and will probably exhibit incorrect behaviour. If this faulty component is built into a system the system may fail. While failure is not always guaranteed, it is likely that errors in specifications will lead to faulty components and faulty components will cause system failure. An error (or mistake) leads to a defect, which can cause an observed failure (Figure 1.1). 9 SOFTWARE TESTING Figure 1.1 Effect of an error Error Defect Failure There are other reasons why systems fail. Environmental conditions such as the presence of radiation, magnetism, electronic fields or pollution can affect the operation of hardware and firmware and lead to system failure. If we want to avoid failure we must either avoid errors and faults or find them and rectify them. Testing can contribute to both avoidance and rectification, as we will see when we have looked at the testing process in a little more detail. One thing is clear: if we wish to influence errors with testing we need to begin testing as soon as we begin making errors – right at the beginning of the development process – and we need to continue testing until we are confident that there will be no serious system failures – right at the end of the development process. Before we move on, let us just remind ourselves of the importance of what we are considering. Incorrect software can harm: yy people (e.g. by causing an aircraft crash in which people die, or by causing a hospital life support system to fail); yy companies (e.g. by causing incorrect billing, which results in the company losing money); yy the environment (e.g. by releasing chemicals or radiation into the atmosphere). Software failures can sometimes cause all three of these at once. The scenario of a train carrying nuclear waste being involved in a crash has been explored to help build public confidence in the safety of transporting nuclear waste by train. A failure of the train’s on-board systems or of the signalling system that controls the train’s movements could lead to catastrophic results. This may not be likely (we hope it is not) but it is a possibility that could be linked with software failure. Software failures, then, can lead to: yy loss of money; yy loss of time; yy loss of business reputation; yy injury; yy death. 10 THE FUNDAMENTALS OF TESTING KEEPING SOFTWARE UNDER CONTROL With all of the examples we have seen so far, what common themes can we identify? There may be several themes that we could draw out of the examples, but one theme is clear: either insufficient testing or the wrong type of testing was done. More and better software testing seems a reasonable aim, but that aim is not quite as simple to achieve as we might expect. Exhaustive testing of complex systems is not possible The launch of the smartphone app occurred at the same time as a new phone hardware platform – the new app was only available on the new hardware for what many would recognise as the market leader at that time. The product launch received extensive world-wide coverage, with the mapping app given a prominent place in launch publicity. In a matter of hours there were tens of thousands of users, and numbers quickly escalated, with many people wanting to see their location in the new app and see how this compared with (for example) Google Maps. Each phone user was an expert in his/ her location – after all they lived there, and ‘test cases’ were generated showing that problems existed. If every possible test had been run, problems would have been detected and rectified prior to the product launch. However, if every test had been run, the testing would still be running now, and the product launch would never have taken place; this illustrates one of the general principles of software testing, which are explained below. With large and complex systems it will never be possible to test everything exhaustively; in fact it is impossible to test even moderately complex systems exhaustively. For the mapping app, it would be unhelpful to say that not enough testing was done; for this particular project, and for many others of similar complexity, that would certainly always be the case. Here the problem was that the right sort of testing was not done because the problems had not been detected. Testing and risk Risk is inherent in all software development. The system may not work or the project to build it may not be completed on time, for example. These uncertainties become more significant as the system complexity and the implications of failure increase. Intuitively, we would expect to test an automatic flight control system more than we would test a video game system. Why? Because the risk is greater. There is a greater probability of failure in the more complex system and the impact of failure is also greater. What we test, and how much we test it, must be related in some way to the risk. Greater risk implies more and better testing. There is much more on risk and risk management in Chapter 5. 11 SOFTWARE TESTING Testing and quality Quality is notoriously hard to define. If a system meets its users’ requirements that constitutes a good starting point. In the examples we looked at earlier the online tax returns system had an obvious functional weakness in allowing one user to view another user’s details. While the user community for such a system is potentially large and disparate, it is hard to imagine any user that would find that situation anything other than unacceptable. In the top 10 criminals example the problem was slightly different. There was no failure of functionality in this case; the system was simply swamped by requests for access. This is an example of a non-functional failure, in that the system was not able to deliver its services to its users because it was not designed to handle the peak load that materialised after radio and TV coverage. The Airbus A380 aircraft problems is an interesting story, because although completed subparts could not be brought together to build an entire aircraft, each of the subparts was ‘correctly manufactured’. Aircraft are increasingly sophisticated, and the A380 aircraft has approximately 530 km of cables, 100,000 wires and 40,300 connectors. Software is used both to design the aircraft and in the manufacture. However, the large subparts were made in two different counties, with different versions of the software in each manufacturing base. So when Airbus was bringing together two halves of the aircraft, the different software meant that the wiring on one did not match the wiring in the other. The cables could not meet up without being changed. Testing may have taken place, but it did not test something as straightforward as the versions of the design software, and whether they were compatible (which in this case they were plainly not). Each large subpart was built according to its own version of the CATIA (Computer Aided Three-Dimensional Interactive Application) software. The result did not give an aircraft that could fly. Of course the software development process, like any other, must balance competing demands for resources. If we need to deliver a system faster (i.e. in less time), for example, it will usually cost more. The items at the corners (or vertices) of the triangle of resources in Figure 1.2 are time, money and quality. These three affect one another, and also influence the features that are or are not included in the delivered software. Figure 1.2 Resources triangle Time Features Money Quality One role for testing is to ensure that key functional and non-functional requirements are examined before the system enters service and any defects are reported to the development team for rectification. Testing cannot directly remove defects, nor can it directly enhance quality. By reporting defects it makes their removal possible and so 12 THE FUNDAMENTALS OF TESTING contributes to the enhanced quality of the system. In addition, the systematic coverage of a software product in testing allows at least some aspects of the quality of the software to be measured. Testing is one component in the overall quality assurance activity that seeks to ensure that systems enter service without defects that can lead to serious failures. Deciding when ‘enough is enough’ How much testing is enough, and how do we decide when to stop testing? We have so far decided that we cannot test everything, even if we would wish to. We also know that every system is subject to risk of one kind or another and that there is a level of quality that is acceptable for a given system. These are the factors we will use to decide how much testing to do. The most important aspect of achieving an acceptable result from a finite and limited amount of testing is prioritisation. Do the most important tests first so that at any time you can be certain that the tests that have been done are more important than the ones still to be done. Even if the testing activity is cut in half it will still be true that the most important testing has been done. The most important tests will be those that test the most important aspects of the system: they will test the most important functions as defined by the users or sponsors of the system, and the most important non-functional behaviour, and they will address the most significant risks. The next most important aspect is setting criteria that will give you an objective test of whether it is safe to stop testing, so that time and all the other pressures do not confuse the outcome. These criteria, usually known as completion criteria, set the standards for the testing activity by defining areas such as how much of the software is to be tested (this is covered in more detail in Chapter 4) and what levels of defects can be tolerated in a delivered product (which is covered in more detail in Chapter 5). Priorities and completion criteria provide a basis for planning (which will be covered in Chapter 2 and Chapter 5) but the triangle of resources in Figure 1.2 still applies. In the end, the desired level of quality and risk may have to be compromised, but our approach ensures that we can still determine how much testing is required to achieve the agreed levels and we can still be certain that any reduction in the time or effort available for testing will not affect the balance – the most important tests will still be those that have already been done whenever we stop. CHECK OF UNDERSTANDING 1. 2. 3. Describe the interaction between errors, defects and failures. Software failures can cause losses. Give three consequences of software failures. What are the vertices of the ‘triangle of resources’? 13 SOFTWARE TESTING WHAT TESTING IS AND WHAT TESTING DOES So far we have worked with an intuitive idea of what testing is. We have recognised that it is an activity used to reduce risk and improve quality by finding defects, which is all true. However, we need to understand a little more about how software testing works in practice before we can think about how to implement effective testing. Testing and debugging Testing and debugging are different kinds of activity, both of which are very important. Debugging is the process that developers go through to identify the cause of bugs or defects in code and undertake corrections. Ideally some check of the correction is made, but this may not extend to checking that other areas of the system have not been inadvertently affected by the correction. Testing, on the other hand, is a systematic exploration of a component or system with the main aim of finding and reporting defects. Testing does not include correction of defects – these are passed on to the developer to correct. Testing does, however, ensure that changes and corrections are checked for their effect on other parts of the component or system. Effective debugging is essential before testing begins to raise the level of quality of the component or system to a level that is worth testing, that is a level that is sufficiently robust to enable rigorous testing to be performed. Debugging does not give confidence that the component or system meets its requirements completely. Testing makes a rigorous examination of the behaviour of a component or system and reports all defects found for the development team to correct. Testing then repeats enough tests to ensure that defect corrections have been effective. So both are needed to achieve a quality result. Static testing and dynamic testing Static testing is the term used for testing where the code is not exercised. This may sound strange, but remember that failures often begin with a human error, namely a mistake in a document such as a specification. We need to test these because errors are much cheaper to fix than defects or failures (as you will see). That is why testing should start as early as possible, another basic principle explained in more detail later in this chapter. Static testing involves techniques such as reviews, which can be effective in preventing defects, for example by removing ambiguities and errors from specification documents; this is a topic in its own right and is covered in detail in Chapter 3. Dynamic testing is the kind that exercises the program under test with some test data, so we speak of test execution in this context. The discipline of software testing encompasses both static and dynamic testing. Testing as a process We have already seen that there is much more to testing than test execution. Before test execution there is some preparatory work to do to design the tests and set them up; after test execution there is some work needed to record the results and check whether the tests are complete. Even more important than this is deciding what we are trying to achieve with the testing and setting clear objectives for each test. A test designed to give confidence that a program functions according to its specification, for example, will be quite different from one designed to find as many defects as possible. We define a test 14 THE FUNDAMENTALS OF TESTING process to ensure that we do not miss critical steps and that we do things in the right order. We will return to this important topic later, where we explain the fundamental test process in detail. Testing as a set of techniques The final challenge is to ensure that the testing we do is effective testing. It might seem paradoxical, but a good test is one that finds a defect if there is one present. A test that finds no defect has consumed resources but added no value; a test that finds a defect has created an opportunity to improve the quality of the product. How do we design tests that find defects? We actually do two things to maximise the effectiveness of the tests. First we use well-proven test design techniques, and a selection of the most important of these is explained in detail in Chapter 4. The techniques are all based on certain testing principles that have been discovered and documented over the years, and these principles are the second mechanism we use to ensure that tests are effective. Even when we cannot apply rigorous test design for some reason (such as time pressures) we can still apply the general principles to guide our testing. We turn to these next. CHECK OF UNDERSTANDING 1. 2. 3. Describe static testing and dynamic testing. What is debugging? What other elements apart from ‘test execution’ are included in ‘testing’? GENERAL TESTING PRINCIPLES Testing is a very complex activity, and the software problems described earlier highlight that it can be difficult to do well. We now describe some general testing principles that help testers, principles that have been developed over the years from a variety of sources. These are not all obvious, but their purpose is to guide testers, and prevent the types of problems described previously. Testers use these principles with the test techniques described in Chapter 4. Testing shows the presence of bugs Running a test through a software system can only show that one or more defects exist. Testing cannot show that the software is error free. Consider whether the top 10 wanted criminals website was error free. There were no functional defects, yet the website failed. In this case the problem was non-functional and the absence of defects was not adequate as a criterion for release of the website into operation. In Chapter 2, we will discuss retesting, when a previously failed test is rerun, to show that under the same conditions, the reported problem no longer exists. In this type of situation, testing can show that one particular problem no longer exists. Although there may be other objectives, usually the main purpose of testing is to find defects. Therefore tests should be designed to find as many defects as possible. 15 SOFTWARE TESTING Exhaustive testing is impossible If testing finds problems, then surely you would expect more testing to find additional problems, until eventually we would have found them all. We discussed exhaustive testing earlier when looking at the smartphone mapping app, and concluded that for large complex systems, exhaustive testing is not possible. However, could it be possible to test small pieces of software exhaustively, and only incorporate exhaustively tested code into large systems? Exhaustive testing – a test approach in which all possible data combinations are used. This includes implicit data combinations present in the state of the software/data at the start of testing. Consider a small piece of software where one can enter a password, specified to contain up to three characters, with no consecutive repeating entries. Using only western alphabetic capital letters and completing all three characters, there are 26 × 26 × 26 input permutations (not all of which will be valid). However, with a standard keyboard, there are not 26 × 26 × 26 permutations, but a much higher number, 256 × 256 × 256, or 224. Even then, the number of possibilities is higher. What happens if three characters are entered, and the ‘delete last character’ right arrow key removes the last two? Are special key combinations accepted, or do they cause system actions (Ctrl + P, for example)? What about entering a character, and waiting 20 minutes before entering the other two characters? It may be the same combination of keystrokes, but the circumstances are different. We can also include the situation where the 20-minute break occurs over the change-of-day interval. It is not possible to say whether there are any defects until all possible input combinations have been tried. Even in this small example, there are many, many possible data combinations to attempt. The number of possible combinations using a smartphone might be significantly less, but it is still large enough to be impractical to use all of them. Unless the application under test (AUT) has an extremely simple logical structure and limited input, it is not possible to test all possible combinations of data input and circumstances. For this reason, risk and priorities are used to concentrate on the most important aspects to test. Both ‘risk’ and ‘priorities’ are covered later in more detail. Their use is important to ensure that the most important parts are tested. Early testing When discussing why software fails, we briefly mentioned the idea of early testing. This principle is important because, as a proposed deployment date approaches, time pressure can increase dramatically. There is a real danger that testing will be squeezed, and this is bad news if the only testing we are doing is after all the development has been completed. The earlier the testing activity is started, the longer the elapsed time available. Testers do not have to wait until software is available to test. Work-products are created throughout the software development life cycle (SDLC). As soon as these are ready, we can test them. In Chapter 2, we will see that requirement documents are the basis for acceptance testing, so the creation of acceptance tests can 16 THE FUNDAMENTALS OF TESTING begin as soon as requirement documents are available. As we create these tests, it will highlight the contents of the requirements. Are individual requirements testable? Can we find ambiguous or missing requirements? Many problems in software systems can be traced back to missing or incorrect requirements. We will look at this in more detail when we discuss reviews in Chapter 3. The use of reviews can break the ‘error–defect–failure’ cycle. In early testing we are trying to find errors and defects before they are passed to the next stage of the development process. Early testing techniques are attempting to show that what is produced as a system specification, for example, accurately reflects that which is in the requirement documents. Ed Kit discusses identifying and eliminating errors at the part of the SDLC in which they are introduced.1 If an error/defect is introduced in the coding activity, it is preferable to detect and correct it at this stage. If a problem is not corrected at the stage in which it is introduced, this leads to what Kit calls ‘errors of migration’. The result is rework. We need to rework not just the part where the mistake was made, but each subsequent part where the error has been replicated. A defect found at acceptance testing where the original mistake was in the requirements will require several work-products to be reworked, and subsequently to be retested. Studies have been done on the cost impacts of errors at the different development stages. While it is difficult to put figures on the relative costs of finding defects at different levels in the SDLC, Table 1.1 does concentrate the mind! Table 1.1 Comparative cost to correct errors Stage error is found Comparative cost Requirements $1 Coding $10 Program testing $100 System testing $1,000 User acceptance testing $10,000 Live running $100,000 This is known as the cost escalation model. What is undoubtedly true is that the graph of the relative cost of early and late identification/ correction of defects rises very steeply (Figure 1.3). The earlier a problem (defect) is found, the less it costs to fix. 1 Kit, E. (1995) Software Testing in the Real World. Addison-Wesley, Reading, MA. 17 SOFTWARE TESTING Cost Figure 1.3 Effect of identification time on cost of errors Time The objectives of various stages of testing can be different. For example, in the review processes, we may focus on whether the documents are consistent and no errors have been introduced when the documents were produced. Other stages of testing can have other objectives. The important point is that testing has defined objectives. One of the drivers behind the push to Agile development methodologies is to enable testing to be incorporated throughout the software build process. This is nothing more than the ‘early testing’ principle. Defect clustering Problems do occur in software. It is a fact. Once testing has identified (most of) the defects in a particular application, it is at first surprising that the spread of defects is not uniform. In a large application, it is often a small number of modules that exhibit the majority of the problems. This can be for a variety of reasons, some of which are: yy System complexity. yy Volatile code. yy The effects of change on change. yy Development staff experience. yy Development staff inexperience. This is the application of the Pareto principle to software testing: approximately 80 per cent of the problems are found in about 20 per cent of the modules. It is useful if testing activity reflects this spread of defects, and targets areas of the application under test where a high proportion of defects can be found. However, it must be remembered that testing should not concentrate exclusively on these parts. There may be fewer defects in the remaining code, but testers still need to search diligently for them. The pesticide paradox Running the same set of tests continually will not continue to find new defects. Developers will soon know that the test team always tests the boundaries of conditions, for 18 THE FUNDAMENTALS OF TESTING example, so they will test these conditions before the software is delivered. This does not make defects elsewhere in the code less likely, so continuing to use the same test set will result in decreasing effectiveness of the tests. Using other techniques will find different defects. For example, a small change to software could be specifically tested and an additional set of tests performed, aimed at showing that no additional problems have been introduced (this is known as regression testing). However, the software may fail in production because the regression tests are no longer relevant to the requirements of the system or the test objectives. Any regression test set needs to change to reflect business needs, and what are now seen as the most important risks. Regression testing will be discussed later in this chapter, but is covered in more detail in Chapter 2. Testing is context dependent Different testing is necessary in different circumstances. A website where information can merely be viewed will be tested in a different way to an ecommerce site, where goods can be bought using credit/debit cards. We need to test an air traffic control system with more rigour than an application for calculating the length of a mortgage. Risk can be a large factor in determining the type of testing that is needed. The higher the possibility of losses, the more we need to invest in testing the software before it is implemented. A fuller discussion of risk is given in Chapter 5. For an ecommerce site, we should concentrate on security aspects. Is it possible to bypass the use of passwords? Can ‘payment’ be made with an invalid credit card, by entering excessive data into the card number field? Security testing is an example of a specialist area, not appropriate for all applications. Such types of testing may require specialist staff and software tools. Test tools are covered in more detail in Chapter 6. Absence of errors fallacy Software with no known errors is not necessarily ready to be shipped. Does the application under test match up to the users’ expectations of it? The fact that no defects are outstanding is not a good reason to ship the software. Before dynamic testing has begun, there are no defects reported against the code delivered. Does this mean that software that has not been tested (but has no outstanding defects against it) can be shipped? We think not. CHECK OF UNDERSTANDING 1. 2. 3. Why is ‘zero defects’ an insufficient guide to software quality? Give three reasons why defect clustering may exist. Briefly justify the idea of early testing. 19 SOFTWARE TESTING FUNDAMENTAL TEST PROCESS We previously determined that testing is a process, discussed above. This process is detailed in what has become known as the fundamental test process, a key element of what testers do, and is applicable at all stages of testing. The most visible part of testing is running one or more tests: test execution. We also have to prepare for running tests, analyse the tests that have been run, and see whether testing is complete. Both planning and analysing are very necessary activities that enhance and amplify the benefits of the test execution itself. It is no good testing without deciding how, when and what to test. Planning is also required for the less formal test approaches such as exploratory testing, covered in more detail in Chapter 4. The fundamental test process consists of five parts that encompass all aspects of testing (Figure 1.4): 1. 2. 3. 4. 5. Planning and control. Analysis and design. Implementation and execution. Evaluating exit criteria and reporting. Test closure activities. Figure 1.4 Fundamental test process Test planning and control Test analysis and design Test implementation and execution Evaluating exit criteria and reporting Test closure activities Although the main activities are in a broad sequence, they are not undertaken in a rigid way. An earlier activity may need to be revisited. A defect found in test execution can sometimes be resolved by adding functionality that was originally not present (either missing in error, or the new facilities are needed to make the other part correct). The new features themselves have to be tested, so even though implementation and execution are in progress, the ‘earlier’ activity of analysis and design has to be performed for the new features (Figure 1.5). 20 THE FUNDAMENTALS OF TESTING Figure 1.5 Iteration of activities Test planning and control Test analysis and design Test implementation and execution Evaluating exit criteria and reporting Test closure activities We sometimes need to do two or more of the main activities in parallel. Time pressure can mean that we begin test execution before all tests have been designed. Test planning and control Planning is determining what is going to be tested, and how this will be achieved. It is where we draw a map; how activities will be done; and who will do them. Test planning is also where we define the test completion criteria. Completion criteria are how we know when testing is finished. Control, on the other hand, is what we do when the activities do not match up with the plans. It is the ongoing activity where we compare the progress against the plan. As progress takes place, we may need to adjust plans to meet the targets, if this is possible. Therefore we need to undertake both planning and control throughout the testing activities. We plan at the outset, but as testing progresses, undertake monitoring and control activities (monitoring to measure what has happened, control to adjust future activities in the light of experience). Monitoring and control feed back into the continual activity of planning. The activities of planning and control are developed in more detail in Chapter 5. Test analysis and design Analysis and design are concerned with the fine detail of what to test (test conditions), and how to combine test conditions into test cases, so that a small number of test cases can cover as many of the test conditions as possible. The analysis and design stage is the bridge between planning and test execution. It is looking backward to the planning (schedules, people, what is going to be tested) and forward to the execution activity (test expected results, what environment will be needed). A part of the design process needs to consider the test data that will be required for the test conditions and test cases that have been drawn up. 21 SOFTWARE TESTING Test design involves predicting how the software under test should behave in a given set of circumstances. Sometimes the expected outcome of a test is trivial: when ordering books from an online book retailer, for instance, under no circumstances should money be refunded to the customer’s card without intervention from a supervisor. If we do not detail expected outcomes before starting test execution, there is a real danger that we will miss the one item of detail that is vital, but wrong. These topics will be discussed in more detail in Chapter 4, when test case design techniques are presented. The main points of this activity are as follows: yy Reviewing requirements, architecture, design, interface specifications and other parts, which collectively comprise the test basis. yy Analysing test items, the specification, behaviour and structure to identify test conditions and test data required. yy Designing the tests, including assigning priority. yy Determining whether the requirements and the system are testable. yy Detailing what the test environment should look like, and whether there are any infrastructure and tools required. yy Highlighting the test data required for the test conditions and test cases. yy Creating bidirectional traceability between test basis and test cases. Test implementation and execution The test implementation and execution activity involves running tests, and this will include where necessary any set-up/tear-down activities for the testing. It will also involve checking the test environment before testing begins. Test execution is the most visible part of testing, but it is not possible without other parts of the fundamental test process. It is not just about running tests. As we have already mentioned, the most important tests need to be run first. How do we know what are the most important tests to run? This is determined during the planning stages, and refined as part of test design. One important aspect undertaken at this stage is combining test cases into an overall run procedure, so that test time can be utilised efficiently. Here the logical ordering of tests is important so that, where possible, the outcome of one test creates the preconditions for one or more tests that are later in the execution sequence. As tests are run, their outcome needs to be logged, and a comparison made between expected results and actual results. Whenever there is a discrepancy between the expected and actual results, this needs to be investigated. If necessary a test incident should be raised. Each incident requires investigation, although corrective action will not be necessary in every case. Test incidents will be discussed in Chapter 5. When anything changes (software, data, installation procedures, user documentation etc.), we need to do two kinds of testing on the software. First of all, tests should be run to make sure that the problem has been fixed. We also need to make sure that the changes have not broken the software elsewhere. These two types are usually called retesting and regression testing, respectively. In retesting we are looking in fine detail at 22 THE FUNDAMENTALS OF TESTING the changed area of functionality, whereas regression testing should cover all the main functions to ensure that no unintended changes have occurred. On a financial system, we should include end of day/end of month/end of year processing, for example, in a regression test pack. Test implementation and execution is where the most visible test activities are undertaken, and usually have the following parts: yy Developing and prioritising test cases, creating test data, writing test procedures and, optionally, preparing test harnesses and writing automated test scripts. yy Collecting test cases into test suites, where tests can be run one after another for efficiency. yy Checking the test environment set-up is correct. yy Running test cases in the determined order. This can be manually or using test execution tools. yy Keeping a log of testing activities, including the outcome (pass/fail) and the versions of software, data, tools and testware (scripts etc.). yy Comparing actual results with expected results. yy Reporting discrepancies as incidents with as much information as possible, including if possible causal analysis (code defect, incorrect test specification, test data error or test execution error). yy Where necessary, repeating test activities when changes have been made following incidents raised. This includes re-execution of a test that previously failed in order to confirm a fix (retesting), execution of a corrected test and execution of previously passed tests to check that defects have not been introduced (regression testing). Evaluating exit criteria and reporting Remember that exit criteria were defined during test planning and before test execution started. At the end of test execution, the test manager checks to see if these have been met. If the criterion was that there would be 85 per cent statement coverage (i.e. 85 per cent of all executable statements have been executed (see Chapter 4 for more detail)), and as a result of execution the figure is 75 per cent, there are two possible actions: change the exit criteria, or run more tests. It is possible that even if the preset criteria were met, more tests would be required. Also, writing a test summary for stakeholders would say what was planned, what was achieved, highlight any differences and in particular things that were not tested. The fourth stage of the fundamental test process, evaluating exit criteria, comprises the following: yy Checking whether the previously determined exit criteria have been met. yy Determining if more tests are needed or if the specified exit criteria need amending. yy Writing up the result of the testing activities for the business sponsors and other stakeholders. 23 SOFTWARE TESTING More detail is given on this subject in Chapter 5. Test closure activities Testing at this stage has finished. Test closure activities concentrate on making sure that everything is tidied away, reports written, defects closed, and those defects deferred for another phase clearly seen to be as such. At the end of testing, the test closure stage is composed of the following: yy Ensuring that the documentation is in order; what has been delivered is defined (it may be more or less than originally planned), closing incidents and raising changes for future deliveries, documenting that the system has been accepted. yy Closing down and archiving the test environment, test infrastructure and testware used. yy Passing over testware to the maintenance team. yy Writing down the lessons learned from this testing project for the future, and incorporating lessons to improve the testing process (‘testing maturity’). The detail of the test closure activities is discussed in Chapter 5. Agile methodologies and the fundamental test process Thus far we have concentrated on ‘traditional’ methodologies when discussing the fundamental test process. We now want to focus on Agile methodologies. The use of Agile methodologies and the relationship with the fundamental test process is not a syllabus topic for the Foundation Certificate, but in the following discussion our understanding of both the fundamental test process and Agile methodologies will grow. We use the term ‘Agile methodologies’ because there is not a single variant or ‘flavour’ of Agile. Any distinctions between these are unimportant here, but the principles are important. Agile software development life cycles aim to have frequent deliveries of software, where each iteration or sprint will build on any previously made available. The aim is to have software that could be implemented into the production environment at the end of each sprint – although a delivery into production might not happen as frequently as this. From the brief introduction to Agile above, it follows that an Agile project has a beginning and an end, but the processes that go between these stages can be repeated many times. Agile projects can be successfully progressing over the course of many months or even years, with a continuous stream of (same length) iterations producing production-quality software, typically every two, three or four weeks. In terms of the fundamental test process, there is a part of the planning and control stage that takes place at the start of the project, and the test closure activities take place at the end of the project. However, some planning and control, and all of the middle three stages of the fundamental test process are present in each and every sprint. 24 THE FUNDAMENTALS OF TESTING Some planning and control activities take place at the beginning of the project. This would typically include resourcing activities, some outline planning on the length of the project, and an initial attempt at ordering the features to be implemented (although this could change significantly as the project progresses, sprint by sprint). Infrastructure planning, together with the identification and provision of any specific testing tools is usually undertaken at this stage, together with a clear understanding within the whole team of what is ‘done’ (i.e. a definition of ‘done’). At the start of each sprint, planning activity takes place, to determine items to include in the sprint. This is a whole team activity based on reaching a consensus of how long each potential deliverable will take. As sprint follows sprint, so the accuracy of estimation increases. The sprint is a fixed length, so throughout the duration of the development, items could be added or removed, to ensure that, at the conclusion, there is tested code ‘on the shelf’ and available for implementation as required. Also the three middle stages of the fundamental test process are accomplished in each sprint. A daily stand-up meeting should result in a short feedback loop, to enable any adjustments to take place and items that prevent progress to be resolved. The whole time for development and testing is limited, so the preparation for testing and the testing itself have to be undertaken in parallel. Towards the end of the sprint, it is possible that most or all of the team are involved in testing, with a focus of delivering all that was agreed at the time of the sprint planning meeting. Automated testing tools are frequently used in Agile projects. Tests can be very low level, and a tester on such a project can provide very useful input to developers in defining tests to be used to identify specific conditions. The earlier in a sprint that this is done the more advantages can be gained within that sprint. The proposed deliverables are sometimes used in conjunction with the definition of ‘done’ to enable a burn-down chart to be drawn up. This enables a track to be kept of progress for all to see – in itself usually a motivating factor. As sprint follows sprint, the subject of regression testing previously delivered, working software becomes more important. Part of the test analysis and design stage will involve selecting regression tests that are appropriate for the current sprint. Tests that previously worked might now (correctly) not pass because the new sprint has changed the intention of previously delivered software. The conclusion of the sprint might often be a sprint review meeting, which can include a demonstration to user representatives and/or the project sponsor. For development using Agile methodologies, the final stage in the fundamental test process – ‘test closure activities’ – is scheduled after the end of the last sprint. This should not be done before, because testing collateral that was used in the last-butthree sprint might no longer be appropriate at the conclusion of the final sprint. As we discussed earlier, even the regression tests might have changed, or a more suitable set of regression tests identified. Further information about Agile methodologies is given in Chapter 2. 25 SOFTWARE TESTING CHECK OF UNDERSTANDING 1. 2. 3. What are the stages in the fundamental test process (in the correct sequence)? Briefly compare regression testing and retesting. When should the expected outcome of a test be defined? THE PSYCHOLOGY OF TESTING A variety of different people may be involved in the total testing effort, and they may be drawn from a broad set of backgrounds. Some will be developers, some professional testers, and some will be specialists, such as those with performance testing skills, while others may be users drafted in to assist with acceptance testing. Who ever is involved in testing needs at least some understanding of the skills and techniques of testing to make an effective contribution to the overall testing effort. Testing can be more effective if it is not undertaken by the individual(s) who wrote the code, for the simple reason that the creator of anything (whether it is software or a work of art) has a special relationship with the created object. The nature of that relationship is such that flaws in the created object are rendered invisible to the creator. For that reason it is important that someone other than the creator should test the object. Of course we do want the developer who builds a component or system to debug it, and even to attempt to test it, but we accept that testing done by that individual cannot be assumed to be complete. Developers can test their own code, but it requires a mindset change, from that of a developer (to prove it works) to that of a tester (trying to show that it does not work). If there are separate individuals involved, there are no potential conflicts of interest. We therefore aim to have the software tested by someone who was not involved in its creation; this approach is called test independence. Below are people who could test software, listed in order of increasing independence: yy Those who wrote the code. yy Members of the same development team. yy Members of a different group (independent test team). yy Members of a different company (a testing consultancy/outsourced). Of course independence comes at a price; it is much more expensive to use a testing consultancy than to test a program oneself. Testers and developers think in different ways. However, although we know that testers should be involved from the beginning, it is not always good to get testers involved in code execution at an early stage; there are advantages and disadvantages. Getting developers to test their own code has advantages (as soon as problems are discovered, they can be fixed, without the need for extensive error logs), but also difficulties (it is hard to find your own mistakes). People and projects have objectives, and we all modify actions to blend in with the goals. If a developer has a goal of producing acceptable software by certain dates, then any testing is aimed towards that goal. 26 THE FUNDAMENTALS OF TESTING If a defect is found in software, the software author may see this as criticism. Testers need to use tact and diplomacy when raising defect reports. Defect reports need to be raised against the software, not against the individual who made the mistake. The mistake may be in the code written, or in one of the documents on which the code is based (requirement documents or system specification). When we raise defects in a constructive way, bad feeling can be avoided. We all need to focus on good communication, and work on team building. Testers and developers are not opposed, but working together, with the joint target of better quality systems. Communication needs to be objective, and expressed in impersonal ways: yy The aim is to work together rather than be confrontational. Keep the focus on delivering a quality product. yy Results should be presented in a non-personal way. The work-product may be wrong, so say this in a non-personal way. yy Attempt to understand how others feel; it is possible to discuss problems and still leave all parties feeling positive. yy At the end of discussions, confirm that you have both understood and been understood. ‘So, am I right in saying that your aim was to deliver on Friday by 12:00, even if you knew there were problems?’ As testers and developers, one of our goals is better quality systems delivered in a timely manner. Good communication between testers and the development teams is one way that this goal can be reached. CHECK OF UNDERSTANDING 1. 2. 3. When testing software, who has the highest level of independence? Contrast the advantages and disadvantages of developers testing their own code. Suggest three ways that confrontation can be avoided. CODE OF ETHICS One last topic that we need to address before we move onto the more detailed coverage of topics in the following chapters is that testers must adhere to a code of ethics: they are required to act in a professional manner. Testers can have access to confidential and/or privileged information, and they are to treat any information with care and attention, and act responsibly to the owner(s) of this information, employers and the wider public interest. Of course, anyone can test software, so the declaration of this code of conduct applies to those who have achieved software testing certification. The code of ethics applies to the following areas: yy Public – certified software testers shall consider the wider public interest in their actions. 27 SOFTWARE TESTING yy Client and employer – certified software testers shall act in the best interests of their client and employer (being consistent with the wider public interest). yy Product – certified software testers shall ensure that the deliverables they provide (for any products and systems they work on) meet the highest professional standards possible. yy Judgement – certified software testers shall maintain integrity and independence in their professional judgement. yy Management – certified software test managers and leaders shall subscribe to and promote an ethical approach to the management of software testing. yy Profession – certified software testers shall advance the integrity and reputation of the profession consistent with the public interest. yy Colleagues – certified software testers shall be fair to and supportive of their colleagues, and promote cooperation with software developers. yy Self – certified software testers shall participate in lifelong learning regarding the practice of their profession, and shall promote an ethical approach to the practice of the profession. The code of ethics is far-reaching in its aims, and a quick review of the eight points reveals interaction with other areas of the syllabus. The implementation of this code of ethics is expanded on in all chapters of this book, and perhaps is the reason for the whole book itself. CHECK OF UNDERSTANDING 1. 2. 3. Why do testers need to consider how they treat the information they use? What eight areas should testers consider when conducting themselves in the workplace? What other sections of this chapter have described how testers should conduct themselves with colleagues? SUMMARY In this chapter, we have looked at key ideas that are used in testing, and introduced some terminology. We examined some of the types of software problems that can occur, and why the blanket explanation of ‘insufficient testing’ is unhelpful. The problems encountered then led us through some questions about the nature of testing, why errors and mistakes are made, and how these can be identified and eliminated. Individual examples enabled us to look at what testing can achieve, and the view that testing does not improve software quality, but provides information about that quality. We have examined both general testing principles and a standard template for testing: the fundamental test process. These are useful and can be effective in identifying the types of problems we considered at the start of the chapter. The chapter finished by examining how developers and testers think, and looked at different levels of test independence, and how testers should behave by adhering to a code of ethics. 28 THE FUNDAMENTALS OF TESTING This chapter is an introduction to testing, and to themes that are developed later in the book. It is a chapter in its own right, but also points to information that will come later. A rereading of this chapter when you have worked through the rest of the book will place all the main topics into context. Example examination questions with answers E1. K1 question Which of the following is correct? Debugging is: a. Testing/checking whether the software performs correctly. b. Checking that a previously reported defect has been corrected. c. Identifying the cause of a defect, repairing the code and checking the fix is correct. d. Checking that no unintended consequences have occurred as a result of a fix. E2. K2 question Which of the following are aids to good communication, and which hinder it? i. ii. iii. iv. v. a. b. c. d. Try to understand how the other person feels. Communicate personal feelings, concentrating on individuals. Confirm the other person has understood what you have said and vice versa. Emphasise the common goal of better quality. Each discussion is a battle to be won. i, ii and iii aid, iv and v hinder. iii, iv and v aid, i and ii hinder. i, iii and iv aid, ii and v hinder. ii, iii and iv aid, i and v hinder. E3. K1 question Which option is part of the ‘implementation and execution’ area of the fundamental test process? a. b. c. d. Developing the tests. Comparing actual and expected results. Writing a test summary. Analysing lessons learnt for future releases. 29 SOFTWARE TESTING E4. K1 question The five parts of the fundamental test process have a broad chronological order. Which of the options gives three different parts in the correct order? a. Implementation and execution, planning and control, analysis and design. b. Analysis and design, evaluating exit criteria and reporting, test closure activities. c. Evaluating exit criteria and reporting, implementation and execution, analysis and design. d. Evaluating exit criteria and reporting, test closure activities, analysis and design. E5. K2 question Which pair of definitions is correct? a. R egression testing is checking that the reported defect has been fixed; retesting is testing that there are no additional problems in previously tested software. b. Regression testing is checking there are no additional problems in previously tested software; retesting enables developers to isolate the problem. c. Regression testing involves running all tests that have been run before; retesting runs new tests. d. Regression testing is checking that there are no additional problems in previously tested software, retesting is demonstrating that the reported defect has been fixed. E6. K1 question Which statement is most true? a. b. c. d. ifferent testing is needed depending on the application. D All software is tested in the same way. A technique that finds defects will always find defects. A technique that has found no defects is not useful. E7. K1 question When is testing complete? a. W hen time and budget are exhausted. b. When there is enough information for sponsors to make an informed decision about release. c. When there are no remaining high priority defects outstanding. d. When every data combination has been exercised successfully. 30 THE FUNDAMENTALS OF TESTING E8. K1 question Which list of levels of tester independence is in the correct order, starting with the most independent first? a. T ests designed by the author; tests designed by another member of the development team; tests designed by someone from a different company. b. Tests designed by someone from a different department within the company; tests designed by the author; tests designed by someone from a different company. c. Tests designed by someone from a different company; tests designed by someone from a different department within the company; tests designed by another member of the development team. d. Tests designed by someone from a different department within the company; tests designed by someone from a different company; tests designed by the author. E9. K2 question The following statements relate to activities that are part of the fundamental test process. i. Evaluating the testability of requirements. ii. Repeating testing activities after changes. iii. Designing the test environment set-up. iv. Developing and prioritising test cases. v. Verifying the environment is set up correctly. Which statement below is true? a. i and ii are part of analysis and design, iii, iv and v implementation and execution. b. i and iii are part of analysis and design, ii, iv and v implementation and execution. c. i and v are part of analysis and design, ii, iii and iv implementation and execution. d. i and iv are part of analysis and design, ii, iii and v implementation and execution. are part of test are part of test are part of test are part of test E10. K2 question Which of the following is true? a. T he developer misunderstood the specification, introducing a mistake into the software that caused a run-time error. b. The specification was incorrect (resulting from a mistake) – this carried forward into the software and resulted in a failure when the code was executed. c. A failure in the writing of the specification gave rise to an error in the code that was implemented. d. A run-time failure in the software was caused by a mistake in the code as written by the developer. 31 SOFTWARE TESTING E11. K1 question Which of the following describes why testing is necessary? a. b. c. d. To show that there are no defects in the software. To reduce the risk of problems occurring when code is implemented. To decide when the software should be implemented. To enable the project plan to be followed. E12. K2 question Which one of the following definition pairs is correct? a. R etesting is rerunning previously successful tests to ensure that there are no unintended consequences; regression testing is ensuring the previously failed test now performs correctly. b. Regression testing is rerunning previously successful tests to ensure that there are no unintended consequences; retesting testing is ensuring the previously failed test now performs correctly. c. Retesting is identifying and correcting the cause of a defect; regression testing is rerunning previously successful tests to ensure that there are no unintended consequences. d. Retesting is rerunning a failed test to identify the cause of the failure; regression testing is selecting the tests that need to be rerun. E13. K1 question How does software testing lead to higher quality? a. b. c. d. By identifying defects, enabling these to be investigated. By preventing software being implemented whilst it is unstable. By ensuring that correct processes are followed. By ensuring software developers know their work will be examined. E14. K2 question When has enough testing been done? a. b. c. d. 32 hen all tests have been run. W When there are no outstanding high priority defects. When the most important tests have been successfully run. When sufficient information is available for sponsors to make an informed decision about release. THE FUNDAMENTALS OF TESTING E15. K1 question Which one of the following is not part of the test analysis and design stage of the fundamental test process? a. b. c. d. Identifying test data to support test conditions and test cases. Creating bidirectional traceability between the test basis and test cases. Examining the testability of the test basis. Verifying that the test environment has been set up correctly. E16. K1 question Why might developer-only testing be less effective than using testing professionals? a. b. c. d. esters have had training in test techniques, developers have not. T Developers are only doing testing because it is one of their assigned tasks. It is harder to see your own errors than those of someone else. Testers have a greater understanding of how the software is meant to work. E17. K2 question Which of the following test objectives are particularly relevant to operational testing? i. ii. iii. iv. v. a. b. c. d. Assessing system reliability. To cause as many failures as possible. To give as much information to stakeholders of the risk of releasing at a given time. Checking that no new defects have been introduced during the development of changes. To provide an assessment of the system availability. i and ii. iii and v. ii and iv. i and v. E18. K1 question Which one item below hinders good communication within the team? a. b. c. d. Try to understand how the other person feels. Communicate personal feelings, concentrating on individuals. Confirm the other person has understood what you have said and vice versa. Emphasise the common goal of better quality. 33 SOFTWARE TESTING E19. K2 question Which of the following are applicable to debugging? i. ii. iii. iv. v. vi. a. b. c. d. 34 Identifying a failure. Performed by a tester. Locating the cause of failure. Fixing the defect. Performed by a developer. Checking the fix has resolved the failure. iii, iv and v. i, ii and iv. i, v and vi. ii, iii and vi. THE FUNDAMENTALS OF TESTING Answers to questions in the chapter SA1. The correct answer is c. SA2. The correct answer is b. SA3. The correct answer is d. Answers to example questions E1. The correct answer is c. a. is a brief definition of testing. b. is retesting. d. is regression testing. E2. The correct answer is c. If you are unsure why, revisit the section in this chapter on the psychology of testing. E3. The correct answer is b. a. is part of ‘analysis and design’. c. is part of ‘evaluating exit criteria and reporting’. d. is part of ‘test closure activities’. E4. The correct answer is b. All other answers have at least one stage of the fundamental test process in the wrong sequence. E5. The correct answer is d. Regression testing is testing that nothing has regressed. Retesting (or confirmation testing) confirms the fix is correct by running the same test after the fix has been made. No other option has both of these as true. E6. The correct answer is a. This is a restatement of the testing principle ‘testing is context dependent’. E7. The correct answer is b. Sometimes time/money does signify the end of testing, but it is really complete when everything that was set out in advance has been achieved. E8. The correct answer is c. This option has someone nearer to the written code in each statement. All other options are not in this order. E9. The correct answer is b. All other answers contain an activity identified as analysis and design that is part of implementation and test execution. E10. The correct answer is b. This relies on the ‘mistake–defect–failure’ or ‘error–fault–failure’ sequence. A mistake is the result of a person – it introduces a defect into the work-product, resulting in a failure when the observed behaviour is not as expected. Other options do not have the correct terms. 35 SOFTWARE TESTING E11. The correct answer is b. It is not possible to show that there are no defects in the software (a). Testing does not decide when software is implemented (c), although the information from testing might help others decide. Option d is not applicable. E12. The correct answer is b. The definitions in b are applicable for retesting and regression testing. If you are unsure, revisit the section in the chapter that goes through these definitions. E13. The correct answer is a. Testing has as a central aim to uncover as many defects as possible. Quality improves as these are uncovered and investigated (and in many cases, fixed). None of the other answers encompasses this central point. E14. The correct answer is d. There being no high priority defects, b is not an indication of enough testing – this might be the case when no tests have been run (and could be the case when the first 10 per cent of tests have been completed). Option a (all tests being run) can be discounted – what about any tests that failed? All high priority tests could have been successfully run, but all the low priority tests might have failed. Option d gives an indication of enough testing – sufficient information is available to enable the sponsors (not ‘testers’) to make a decision based on the information provided. E15. The correct answer is d. Verifying that the test environment has been set up is part of the test implementation and execution stage of the fundamental test process. E16. The correct answer is c. Testers bring a sense of ‘independence’, and do not have the same assumptions as any developer who created the software. E17. The correct answer is d. Other answers give objectives for other phases of testing: finding as many defects as possible is development testing; giving information to assess the risk of releasing is acceptance testing; and checking no defects have been introduced during the development of a change is maintenance testing. E18. The correct answer is b. The other options help good communication within the overall team. E19. The correct answer is a. All other answers contain something that is more appropriate to ‘testing’ rather than ‘debugging’. 36 2 LIFE CYCLES Angelina Samaroo INTRODUCTION In the previous chapter, we looked at testing as a concept – what it is and why we should do it. In this chapter we will look at testing as part of overall software development. Clearly testing does not take place in isolation; there must be a product first. We will refer to work-products and products. A work-product is an intermediate deliverable required to create the final product. Work-products can be documentation or code. The code and associated documentation will become the product when the system is declared ready for release. In software development, work-products are generally created in a series of defined stages, from capturing a customer requirement, to creating the system, to delivering the system. These stages are usually shown as steps within a software development life cycle. In this chapter we will look at two life cycle models – sequential and iterative. For each one, the testing process will be described, and the objectives at each stage of testing explained. Finally, we will look at the different types of testing that can take place throughout the development life cycle. Learning objectives The learning objectives for each section are as follows. Each section has been categorised as K2 overall, but individual K1 elements are shown where applicable. Software development models (K2) yy Understanding of the relationship between development, test activities and work-products in the development life cycle, giving examples based on project and product characteristics and context. yy Recognition that software development models must be adapted to the context of project and product characteristics. (K1) yy Recall of reasons for different levels of testing, and characteristics of good testing in any life cycle model. (K1) 37 SOFTWARE TESTING Test levels (K2) yy Be able to compare the different levels of testing, considering for each the: Major objectives. Typical objectives of testing. Typical targets of testing (e.g. functi