Structured Testing - McCabe and Associates

6 The Baseline Method
The baseline method, described in this section, is a technique for identifying a set of control
paths to satisfy the structured testing criterion. The technique results in a basis set of test
paths through the module being tested, equal in number to the cyclomatic complexity of the
module. As discussed in section 2, the paths in a basis are independent and generate all paths
via linear combinations. Note that “the baseline method” is different from “basis path testing.”
Basis path testing, another name for structured testing, is the requirement that a basis set
of paths should be tested. The baseline method is one way to derive a basis set of paths. The
word “baseline” comes from the first path, which is typically selected by the tester to represent
the “baseline” functionality of the module. The baseline method provides support for
structured testing, since it gives a specific technique to identify an adequate test set rather than
resorting to trial and error until the criterion is satisfied.
6.1 Generating a basis set of paths
The idea is to start with a baseline path, then vary exactly one decision outcome to generate
each successive path until all decision outcomes have been varied, at which time a basis will
have been generated. To understand the mathematics behind the technique, a simplified version
of the method will be presented and prove that it generates a basis [WATSON5]. Then,
the general technique that gives more freedom to the tester when selecting paths will be
described. Poole describes and analyzes an independently derived variant in [NIST5737].
6.2 The simplified baseline method
To facilitate the proof of correctness, the method will be described in mathematical terms.
Readers not interested in theory may prefer to skip to section 6.3 where a more practical presentation
of the technique is given.
In addition to a basis set of paths, which is a basis for the rows of the path/edge matrix if all
possible paths were represented, it is possible to also consider a basis set of edges, which is a
basis for the columns of the same matrix. Since row rank equals column rank, the cyclomatic
complexity is also the number of edges in every edge basis. The overall approach of this section
is to first select a basis set of edges, then use that set in the algorithm to generate each
successive path, and finally use the resulting path/edge matrix restricted to basis columns to
show that the set of generated paths is a basis.
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