Precondition Coverage in Software Testing

Preconditions indicate when it is permitted to use a given function. However, it is not always the case that both outcomes of a precondition are observed during testing. A precondition that is always false makes a function unusable, a precondition that is always true may turn out to be actually an invariant. In model-based testing, preconditions describes when a transition may be executed from a given state. If no outgoing transition is enabled in a given state because all preconditions of all outgoing transitions are false, the test model may be flawed. Experiments show a low test coverage of preconditions in the Scala library. We also investigate preconditions in Modbat models for model-based testing, in that case, a certain number of test cases is needed to produce sufficient coverage, but remaining cases of low coverage indeed point to legitimate flaws in test models or code.