1

Chapter 8:

Verification & Validation

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 22.1-22.2

3

Costs of finding and fixing defects late..

Delays in identifying and fixing

defects get more expensive as the

lifecycle progresses!

$1

$10

$100

$1000

Co

st

of

Fix

ing

a D

efe

ct

Defe

cts

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

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

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

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

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

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

V&V Techniques

Techniques

Static Methods

Techniques applied to artifacts without

execution.

Inspections and Reviews

DynamicMethods

Techniques applied to artifacts through

execution.

Testing

11

Static and Dynamic V&V

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

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

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

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.

• 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 Vs Debugging

What do you think is the difference?

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

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

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.