Abstract: A method of testing a software module using a genetic algorithm to generate a best test script is provided. The software module has a number of possible states. A set of state machines is created which represent a definition for either a user interface or an application program interface (API) of the software module in terms of the possible states. From the state machines, a set of test cases is automatically generated, such that each test case consists of code for manipulating the user interface or API. A genetic algorithm creates populations of test scripts from the test cases, in which each test script includes a number of test cases. Each test script from each successive generation of test scripts is executed by applying the script as input to the software module. A code coverage analyzer provides a measure of code coverage to the genetic algorithm for each test script.