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Chapter 8 – Software Testing

Topics covered  Development testing  Test-driven development  Release testing  User testing

Program testing goals  To demonstrate to the developer and the customer that the software meets its requirements. ▪ For custom software, this means that there should be at least one test for every requirement in the requirements document. For generic software products, it means that there should be tests for all of the system features, plus combinations of these features , that will be incorporated in the product release.  To discover situations in which the behavior of the software is incorrect, undesirable or does not conform to its specification. ▪ Defect testing is concerned with rooting out undesirable system behavior such as system crashes, unwanted interactions with other systems, incorrect computations and data corruption.

Validation and defect testing  The first goal leads to validation testing ▪ You expect the system to perform correctly using a given set of test cases that reflect the system’s expected use.  The second goal leads to defect testing ▪ The test cases are designed to expose defects. The test cases in defect testing can be deliberately obscure and need not reflect how the system is normally used.

An input-output model of program testing

Verification vs validation  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.

Inspections and testing  Software inspections Concerned with analysis of the static system representation to discover problems ( static verification ) ▪ May be supplement by tool-based document and code analysis. ▪ Discussed in Chapter 15.  Software testing Concerned with exercising and observing product behaviour ( dynamic verification ) ▪ The system is executed with test data and its operational behaviour is observed.

Inspections and testing

Advantages of inspections  During testing, errors can mask (hide) other errors. Because inspection is a static process, you don’t have to be concerned with interactions between errors.  Incomplete versions of a system can be inspected without additional costs. If a program is incomplete , then you need to develop specialized test harnesses to test the parts that are available.  As well as searching for program defects, an inspection can also consider broader quality attributes of a program, such as compliance with standards, portability and maintainability.

Inspections and testing  Inspections and testing are complementary and not opposing verification techniques.  Both should be used during the V & V process.  Inspections cannot check non-functional characteristics such as performance, usability, etc.

Stages of testing  Development testing , where the system is tested during development to discover bugs and defects.  Release testing , where a separate testing team test a complete version of the system before it is released to users.  User testing , where users or potential users of a system test the system in their own environment.

Development testing

Unit testing  Unit testing is the process of testing individual components in isolation.  It is a defect testing process.  Units may be: ▪ Individual functions or methods within an object ▪ Object classes with several attributes and methods

Object class testing  Complete test coverage of a class involves ▪ Testing all operations associated with an object ▪ Setting and interrogating all object attributes ▪ Exercising the object in all possible states.  Inheritance makes it more difficult to design object class tests as the information to be tested is not localised.