In one embodiment, constructing one or more sets of variables corresponding to one or more input variables of a software module respectively; for each one of the sets of variables, computing an average branching depth that is affected by the set of variables; selecting a first one of the sets of variables that has the smallest average branching depth; assigning a first symbolic value to the input variable of the first set of variables; symbolically executing the software module to generate a first set of test cases for the first set of variables; optionally compacting the first set of test cases by removing the redundant tests that do not increase test coverage and selecting a minimal subset of the first set of test cases that cover all the covered conditional branch points; and validating the software module using the first set of test cases.