Introduction to Software Testing

Like other software, tests can be designed in an abstract way. However, as discussed at length in Chapter 4, developers want tests to become “real” as soon as possible so that they can benefit from the immediate feedback of any failed tests. To do so, all the code must compile, tests must not cause collateral damage, the process must be repeatable, and it must complete in a timely manner. Unit testing normally doesn't pose a serious challenge with respect to these constraints, but other test phases certainly do. This section discusses technical problems that arise during the implementation of test cases. We do not catalog the problems from a process point of view. Instead, we focus on the technical strategies used to solve these problems. Many of the problems arise naturally during software integration, but integration is not the only source of difficulty; the testing of fully integrated systems also requires the techniques discussed here.

Software programs are composed of many pieces of software of varying sizes. Individual programmers are often responsible for testing the lowest level components (classes, modules, and methods). After that, testing must be carried out in collaboration with software integration. Software can be integrated in many ways.

Integration testing is the testing of incompatibilities and interfaces between otherwise correctly working components. That is, it is the testing needed to assure correct integration of subcomponents into a bigger working component. This is emphatically not the same as testing an already integrated component.

Integration testing is often done with an incomplete system. The tester may be evaluating how only two of many components in the system work together, may be testing integration aspects before the full system is complete, or may be putting the system together piece by piece and evaluating how each new component fits with the previously integrated components.

This chapter uses the term software “component” in a very broad sense: A component is a piece of a program that can be tested independently of the complete program or system. Thus, classes, modules, methods, packages, and even code fragments can be considered to be components. Also, non-executable software artifacts such as XML files, XML schemas, and databases can be considered to be components.