This chapter is extracted from Sommerville’s slides. Textbook chapter

Objectives To introduce software verification and validation and to discuss the distinction between them. To describe the program inspection process and its role in V & V. 2 2

3 Costs of Finding and Fixing Late Delays in identifying and fixing defects gets geometrically more expensive as the lifecycle progresses! $1 $10 $100 $1000 Cost of Fixing a Defect Defects Time in (Phase of) Development

V and 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. 4

V and V Process 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 useful and useable in an operational situation. 5

What’s 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

Verification Verification is any checking process conducted on software artifacts 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. 7

Validation Validation is the process of evaluating software artifacts 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. 8

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

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

Static and Dynamic V&V 11

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 12

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. 13

Testing Concerned with exercising and observing product behaviour (dynamic verification) The system is executed with test data and its operational behaviour is observed 14

Testing 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

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

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

Defect Testing and Debugging What do you think is the difference? 18

A comparison Testing Concerned with establishing the existence of defects in a program. Debugging Concerned with locating and repairing errors. 19

The Debugging Process 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. 21

The V-Model of Development 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

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. 24

Reading for next lecture For the next lecture, please read your assigned topic from the textbook. We will have a discussion next session and it is important that you read your section. 25