In recent years, we see a growing awareness to the importance of assessing the quality of specifications. In the context of model checking, this can be done by analyzing the effect of applying mutations to the specification or the system. If the system satisfies the mutated specification, we know that some elements of the specification do not play a role in its satisfaction, thus the specification is satisfied in some
way. If the mutated system satisfies the specification, we know that some elements of the system are not
by the specification. Coverage in model checking has been adopted from the area of testing, where coverage information is crucial in measuring the exhaustiveness of test suits. It is now time for model checking to pay back, and let testing enjoy the rich theory and applications of vacuity. We define and study vacuous satisfaction in the context of testing, and demonstrate how vacuity analysis can lead to better specifications and test suits.