6.0 The Need for Levels of Testing

Execution-based software testing, especially for large systems, is usually carried out at different levels. In most cases there will be 3 4 levels, or major phases of testing: unit test, integration test, system test, and some type of acceptance test as shown in Figure 6.1. Each of these may consist of one or more sublevels or phases. At each level there are specific testing goals. For example, at unit test a single component is tested. A principal goal is to detect functional and structural defects in the unit. At the integration level several components are tested as a group, and the tester investigates component interactions. At the system level the system as a whole is tested and a principle goal is to evaluate attributes such as usability, reliability, and performance.

Figure 6.1: Levels of testing

An orderly progression of testing levels is described in this chapter for both object-oriented and procedural-based software systems. The major testing levels for both types of system are similar. However, the nature of the code that results from each developmental approach demands different testing strategies, for example, to identify individual components, and to assemble them into subsystems. The issues involved are described in Sections 6.0.1, 6.1, and 6.2.3 of this chapter. For both types of systems the testing process begins with the smallest units or components to identify functional and structural defects. Both white and black box test strategies as discussed in Chapters 4 and 5 can be used...