This chapter introduces the major test coverage criteria in use today. It starts out in a very theoretical way, but a firm grasp of the theoretical aspects of graphs and graph coverage makes the remainder of the chapter simpler. We first emphasize a generic view of a graph without regard to the graph's source. After this model is established, the rest of the chapter turns to practical applications by demonstrating how graphs can be obtained from various software artifacts and how the generic versions of the criteria are adapted to those graphs.

OVERVIEW

Directed graphs form the foundation for many coverage criteria. Given an artifact under test, the idea is to obtain a graph abstraction of that artifact. For example, the most common graph abstraction for source code maps code to a control flow graph. It is important to understand that the graph is not the same as the artifact, and that, indeed, artifacts typically have several useful, but nonetheless quite different, graph abstractions. The same abstraction that produces the graph from the artifact also maps test cases for the artifact to paths in the graph. Accordingly, a graphbased coverage criterion evaluates a test set for an artifact in terms of how the paths corresponding to the test cases “cover” the artifact's graph abstraction.

We give our basic notion of a graph below and will add additional structures later in the chapter when needed.