[en] The design criteria of the software module were based on complexity of the module and the cohesion of the module. The easiness of detection of a fault in the software module can be an additional candidate for the module design criteria. The module test coverage criteria and test case generation is reviewed from the aspects of module testability, easiness of the fault detection. One of the methods is making the numerical results as output in addition to the logical outputs. With modules designed with high testability, the test case generation and test coverage can be made more effective