In engineering, as in baseball, you don't have to be strong to hit a home run. You just have to hit it dead center.
This chapter introduces some of the most widely known test coverage criteria. This chapter uses graphs to define criteria and design tests. This starts our progression into the RIPR model by ensuring that tests “reach” certain locations in a graph model of the artifact being tested. The chapter starts with basic theory as a way to make the practical and applied portions of the chapter easier to follow. 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. They come from many sources and types of software artifacts, including control flow graphs from source, design structures, finite state machines, statecharts, and use cases, among others. We use the term artifact in the most general way, to be anything associated with the software, including the requirements, design documents, implementation, tests, user manuals, and many others. Graph criteria usually require the tester to “cover” the graph in some way, usually by traversing specific portions of the graph. This overview presents graphs in general terms, and overlaps standard texts on discrete math, algorithms, and graph theory. Unlike those theoretical treatments, we focus only on the ideas needed for testing and introduce some new terminology that enable test design.
Given an artifact under test, the idea is to extract a graph from that artifact. For example, the most common graph abstraction for source code maps executable statements and branches to a control flow graph. It is important to recognize that the graph is not the same as the artifact, and usually omits certain details. It is also possible for the same artifact to have several useful, but 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 graph-based 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.
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