Verification and ValidationVerification vs validationThe V & V processStatic and dynamic verificationStatic and dynamic V&VProgram testingTypes of testingV& V goalsV & V confidenceTesting and debuggingThe debugging processV & V planningThe V-model of developmentThe structure of a software test planSoftware inspectionsInspection successInspections and testingProgram inspectionsInspection pre-conditionsThe inspection processInspection procedureInspection teamsInspection checklistsInspection checksAutomated static analysisStatic analysis checksStages of static analysisSlide 28LINT static analysisUse of static analysisCleanroom software developmentThe Cleanroom processCleanroom process characteristicsIncremental developmentFormal specification and inspectionsCleanroom process teamsCleanroom process evaluationKey pointsSlide 39©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 1Verification and ValidationAssuring that a software system meets a user's needs©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 2Verification: "Are we building the product right"The software should conform to its specificationValidation: "Are we building the right product"The software should do what the user really requiresVerification vs validation©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 3Is a whole life-cycle process - V & V must be applied at each stage in the software process.Has two principal objectives•The discovery of defects in a system•The assessment of whether or not the system is usable in an operational situation.The V & V process©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 4Software inspections Concerned with analysis of the static system representation to discover problems (static verification)•May be supplemented by tool-based document and code analysisSoftware testing Concerned with exercising and observing product behaviour (dynamic verification)•The system is executed with test data and its operational behaviour is observedStatic and dynamic verification©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 5Static and dynamic V&VFormalspecificationHigh-leveldesignRequirementsspecificationDetaileddesignProgramPrototypeDynamicvalidationStaticverification©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 6Can reveal the presence of errors NOT their absenceA successful test is a test which discovers one or more errorsThe only validation technique for non-functional requirementsShould be used in conjunction with static verification to provide full V&V coverageProgram testing©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 7Defect testing•Tests designed to discover system defects.•A successful defect test is one which reveals the presence of defects in a system.•Covered in Chapter 20 Statistical testing•tests designed to reflect the frequence of user inputs. Used for reliability estimation.•Covered in Chapter 21 Types of testing©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 8V& V goalsVerification and validation should establish confidence that the software is fit for purposeThis does NOT mean completely free of defectsRather, it must be good enough for its intended use and the type of use will determine the degree of confidence that is needed©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 9V & V confidenceDepends on system’s purpose, user expectations and marketing environment•Software function»The level of confidence depends on how critical the software is to an organisation•User expectations»Users may have low expectations of certain kinds of software•Marketing environment»Getting a product to market early may be more important than finding defects in the program©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 10Defect testing and debugging are distinct processesVerification and validation is concerned with establishing the existence of defects in a programDebugging is concerned with locating and repairing these errorsDebugging involves formulating a hypothesis about program behaviour then testing these hypotheses to find the system errorTesting and debugging©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 11The debugging processLocateerrorDesignerror repairRepairerrorRe-testprogramTestresultsSpecificationTestcases©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 12Careful planning is required to get the most out of testing and inspection processesPlanning should start early in the development processThe plan should identify the balance between static verification and testingTest planning is about defining standards for the testing process rather than describing product testsV & V planning©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 13The V-model of developmentRequirementsspecificationSystemspecificationSystemdesignDetaileddesignModule andunit codeand tessSub-systemintegrationtest planSystemintegrationtest planAcceptancetest planServiceAcceptancetestSystemintegration testSub-systemintegration test©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 14The structure of a software test planThe testing processRequirements traceabilityTested itemsTesting scheduleTest recording proceduresHardware and software requirementsConstraints©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 15Software inspectionsInvolve people examining the source representation with the aim of discovering anomalies and defectsDo not require execution of a system so may be used before implementationMay be applied to any representation of the system (requirements, design, test data, etc.)Very effective technique for discovering errors©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 16Inspection successMany different defects may be discovered in a single inspection. In testing, one defect ,may mask another so several executions are requiredThey reuse domain and programming knowledge so reviewers are likely to have seen the types of error that commonly arise©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 19 Slide 17Inspections and