The Art of Software Testing, Second Edition

6.1. Function Testing

As indicated in Figure 6.3, function testing is a process of attempting to find discrepancies between the program and the external specification. An external specification is a precise description of the program's behavior from the point of view of the end user.

Except when used on small programs, function testing is normally a black-box activity. That is, you rely on the earlier module-testing process to achieve the desired white-box logic-coverage criteria.

To perform a function test, the specification is analyzed to derive a set of test cases. The equivalence-partitioning, boundary-value analysis, cause-effect graphing, and error-guessing methods described in Chapter 4 are especially pertinent to function testing. In fact, the examples in Chapter 4 are examples of function tests. The descriptions of the FORTRAN DIMENSION statement, the examination-scoring program, and the DISPLAY command actually are examples of external specifications. (Note, however, that they are not completely realistic examples; for instance, a real external specification for the scoring program would include a precise description of the format of the reports.) Hence, no examples of function tests are presented in this section.

Many of the guidelines of Chapter 2 also are particularly pertinent to function testing. Keep track of which functions have exhibited the greatest number of errors; this information is valuable because it tells us that these functions probably also contain ...