November 2005J. B. Wordsworth: J5DAMQVT1 Design and Method Quality, Verification, and Testing

November 2005J. B. Wordsworth: J5DAMQVT2 Objectives Explain the meaning of quality as it applies to the various stages of the development of a software product. Distinguish validation from verification. Explain the purpose of testing. Distinguish black box testing from white box testing.

November 2005J. B. Wordsworth: J5DAMQVT3 Quality Fitness for purpose – meeting the requirements –For a system – whether the customer is satisfied –For a FID function – whether it meets its specification –For an O-O class – whether it behaves as specified

November 2005J. B. Wordsworth: J5DAMQVT4 Quality attributes Customer-driven: –Usable –Reliable –Functionally correct Developer-driven: –Testable –Maintainable –Well-documented

November 2005J. B. Wordsworth: J5DAMQVT5 Validation Comparing informal requirements with precise proposals Requirements with use cases FID functions with use cases

November 2005J. B. Wordsworth: J5DAMQVT6 Verification Formal or informal? Specification against Design Design against Code Specifications of functions against sequence diagrams

November 2005J. B. Wordsworth: J5DAMQVT7 Aims of testing Find errors, and correct them. Convince the customer that the product is a good one. Help with the evolution of the product.

November 2005J. B. Wordsworth: J5DAMQVT8 Levels of testing Acceptance –Usability –Function –Performance –Stress System Integration Module Regression

November 2005J. B. Wordsworth: J5DAMQVT9 Testing principles Find errors in a program by executing it. What is an error? – a result that does not meet the user’s expectations. A good test case is one with a high probability of finding an error that is as yet undiscovered. Testing should be conducted by an independent third party.

November 2005J. B. Wordsworth: J5DAMQVT10 Testability observability –distinct output for each input –past and present states are visible –incorrect output is easily identifiable. controllability –all possible outputs can be generated –all code is executable –input and output format consistent and structured –states and variables can be directly controlled.

November 2005J. B. Wordsworth: J5DAMQVT11 Limitations of testing Testing can only show that errors are present. Not finding an error by testing doesn’t mean that there aren’t any. Testing can only be effective if you have an objective definition of an error. Formal specifications are more objective than specifications in a natural language. Pareto principle: 80% of the errors are in 20% of the modules.

November 2005J. B. Wordsworth: J5DAMQVT12 Black box and white box Black box testing begins with the specification: –equivalence partitions –boundary values White box testing begins with the code: –if-then-else tests: true and false –switch: all cases –loops: no iterations, several iterations, too many iterations –data: all possible values, some impossible values –boundary values

November 2005J. B. Wordsworth: J5DAMQVT13 Summary Quality is determined by a product’s fitness for its purpose, as determined by its customers. Verification compares a product’s specification with its implementation. Testing is a means of assessing a product’s quality by examining its behaviour.