SEN4013 LECTURE NOTES, Lecture notes of Software Engineering

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SEN

Software Verification and

Validation

Lecture 1

Software Test and Analysis in a Nutshell

Learning

Objectives

View the “big picture'' of software

quality in the context of a software

development project and

organization:

Introduce the range of software

verification and validation activities –

cursory and incomplete

Provide a rationale for selecting and

combining them within a software

development process.

Verification and Design

Activities

Verification and design activities take

various forms

• suited to highly repetitive construction of

non-critical items for mass markets

highly customized or highly critical

products.

Appropriate verification activities

depend on

• engineering discipline
• construction process
• final product
• quality requirements.

Non – Critical or Critical

Products

Repetition and high levels of

automation in production

lines reduces the need for

verification of individual

products.

A few key components are

verified.

Full test is not economical

depending on the costs of

testing, the reliability of

the production process

Non – Critical or Critical

Products

Some products are not built in

series but are engineered

individually through highly

evolved processes and tools.

Each product is at least partly

unique in its design and

functionality.

Verified both during and after

production to identify and

eliminate faults.

Verificati

on

Verification depends

on

how the product is

produced

• in series
• individually

Complexity of the

product

Why to Verify

Software?

Why to Verify

Software?

Cost of

Verification

The cost of software verification often

exceeds half the overall cost of

development and maintainance.

Relative cost of

bugs

“bugs found later cost more to fix”

Cost to fix a bug increases

exponentially (10x)

• i.e., it increases tenfold as time increases

E.g., a bug found during specification

costs $1 to fix.

… if found in design cost is $

… if found in code cost is $

… if found in released software cost is

Variety of

Approaches

There are no fixed recipes

Test designers must

• choose and schedule the right blend of

techniques

• to reach the required level of quality
• within cost constraints

design a specific solution that suits

the problem

the requirements

• the development environment

Five Basic

Questions

1. When do verification and

validation start? When are they

complete?

2. What particular techniques should

be applied during development?

3. How can we assess the readiness of

a product?

4. How can we control the quality of

successive releases?

5. How can the development process

itself be improved?

Early start: from

feasibility study

The feasibility study of a new project

must take into account the required

qualities and their impact on the overall

cost

At this stage, quality related activities

include

risk analysis

• measures needed to assess and control

quality at each stage of development.

assessment of the impact of new

features and new quality requirements

contribution of quality control activities to

development cost and schedule.

Long lasting: beyond

maintenance

Maintenance activities include

• analysis of changes and extensions

generation of new test suites for

the added functionalities

• re-executions of tests to check for non

regression of software functionalities after

changes and extensions

fault tracking and analysis