Chapter 8: Verification & Validation

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Esmond Moore
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1 1 Chapter 8: Verification & Validation

2 2 Objectives To introduce software verification and validation and discuss the distinctions between them. V&V: Verification & Validation To describe the program inspection process and its role in V&V. Chapter 22 in the Sommerville textbook, Section

3 Cost of Fixing a Defect 3 Costs of finding and fixing defects late.. $1000 Delays in identifying and fixing defects get more expensive as the lifecycle progresses! $100 Defects $10 $1

4 4 V&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. Confidence depends on: Software function User expectations Marketing environment

5 5 What is the difference? 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 requires. (Fit for use)

6 6 V&V Process Is a whole life-cycle process - V & V must be applied at each stage in the software process. Approaches: Inspections & Testing Has two principal objectives The discovery of defects in a system; The assessment of whether or not the system is useful and useable in an operational situation.

7 7 Verification Verification is any checking process conducted on software artefacts in an attempt to determine if they work as specified by the designers of the system. Includes reviews, inspections, walkthroughs, unit testing and integration testing.

8 8 Validation Validation is the process of evaluating software artefacts during the software development process in an attempt to determine if the system works as required by the customers. Includes program reviews, system testing, customer acceptance testing.

9 9 A comparison (purpose) Verification Main purpose is to detect defects in the artefacts of the system under development. Validation Main purpose is to show that the system under development meets user needs, requirements, and expectations.

10 10 V&V Techniques Techniques Static Methods Dynamic Methods Techniques applied to artifacts without execution. Inspections and Reviews Techniques applied to artifacts through execution. Testing

11 Static and Dynamic V&V 11

12 12 Inspections or Reviews Concerned with analysis of the static system representation to discover problems (static verification) May be supplement by tool-based document and code analysis

13 13 Inspections These involve people examining the source representation with the aim of discovering anomalies and defects. (using checklists) Inspections do not require execution of a system so may be used before implementation. They may be applied to any representation of the system such as the requirements or design. They have been shown to be an effective technique for discovering program errors.

14 14 Testing Concerned with exercising and observing product behaviour (dynamic verification) The system is executed with test data and its operational behaviour is observed Can reveal the presence of errors NOT their absence. The only validation technique for non-functional requirements as the software has to be executed to see how it behaves. Should be used in conjunction with static verification to provide full V&V coverage.

15 15 Types of Testing Defect testing & Validation testing What s the difference? What s a successful defect test? And what s a successful validation test?

16 Defect Testing Vs Validation A comparison.. Defect Testing Tests designed to discover system defects. A successful defect test is one which reveals the presence of defects in a system.

16 16 Defect Testing Vs Validation A comparison.. 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 10 Validation Testing Intended to show that the software meets its requirements. A successful test is one that shows that a requirements has been properly implemented.

17 17 Defect Testing Vs Debugging What do you think is the difference?

18 18 Defect Testing Vs Debugging A comparison.. Defect Testing Concerned with establishing the existence of defects in a program. Debugging Concerned with locating and repairing errors.

19 Debugging Process 19

20 20 Validation and Verification Planning 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 tests. IEEE Standard Test Plan

21 V-Model of Development 21

22 22 Advantages of Inspections over Testing Many different defects may be discovered in a single inspection. In testing, one defect,may mask another (interaction between errors) so several executions are required. Incomplete versions of the software can be inspected without additional costs. Inspections consider broader SW quality attributes such as compliance with standards, poor programming style, inappropriate algorithms, etc.

23 23 Inspections and Testing Inspections and testing are complementary and not opposing verification techniques. Both should be used during the V & V process. Inspections can check conformance with a specification but not conformance with the customer s real requirements. Inspections cannot check non-functional characteristics such as performance, usability, etc.

SWEN 256 Software Process & Project Management

SWEN 256 Software Process & Project Management What is quality? A definition of quality should emphasize three important points: 1. Software requirements are the foundation from which quality is measured.