How is cyclomatic complexity useful in program test?

Cyclomatic complexity calculates the amount of decision logic in a single software module. It is used for two related purposes in the structured testing methodology. First, it gives the number of recommended tests for software. Second, it is used during all phases of the software lifecycle, starting with design, to keep software reliable, testable, and manageable. Cyclomatic complexity is based entirely on the structure of software's control flow graph.