A Study of Test Coverage Adequacy In the Presence of Stubs

The purpose of implementation-based testing is to gain a measure of confidence in the correctness of the software by providing adequate coverage of the code. One unit of testing in object-oriented software is a class. However, classes use other classes and if class interactions form a cycle of dependencies then, to test a client class that uses an untested supplier class, stubs must be constructed to simulate the correct behavior of the untested supplier class. However, an important consideration in using stubs to facilitate testing of a client class is the adequacy of code coverage in the client when the client uses a stub rather than the actual supplier class. In this paper we present a study of test coverage adequacy in the presence of stubs as used to facilitate testing of an object-oriented application. We examine coverage in both cluster and class-based testing of the application and, using the results of our study, we draw some conclusions about the coverage provided when stubs are used in each form of testing. In addition, we study the ability of the tester to meet the specified adequacy criteria for class-based testing in the presence of stubs.