Deriving Test Cases

Deriving Test Cases

The basis path testing method can be applied to a procedural design or to source code. In this section, we present basis path testing as a series of steps. The procedure average, depicted in PDL in Figure 17.4, will be used as an example to illustrate each step in the test case design method. Note that average, although an extremely simple algorithm, contains compound conditions and loops. The following steps can be applied to derive the basis set:

1.Using the design or code as a foundation, draw a corresponding flow graph.
A flow graph is created using the symbols and construction rules presented in Section 16.4.1. Referring to the PDL for average in Figure 17.4, a flow graph is created by numbering those PDL statements that will be mapped into corresponding flow graph nodes. The corresponding flow graph is in Figure 17.5.

2. Determine the cyclomatic complexity of the resultant flow graph.

The cyclomatic complexity, V(G), is determined by applying the algorithms described in Section 17.5.2. It should be noted that V(G) can be determined without developing a flow graph by counting all conditional statements in the PDL (for the procedure average, compound conditions count as two) and adding 1. Referring to Figure 17.5,

V(G) = 6 regions
V(G) = 17 edges _ 13 nodes + 2 = 6
V(G) = 5 predicate nodes + 1 = 6