Model-based test case generation allows one to derive almost arbitrary numbers of test cases from models. If resulting test suites are executed against real implementations, there are often huge numbers of failed test cases. Thus, the analysis of the test execution, i.e. the identification of failures for error reporting, becomes a tedious and time consuming task. In this paper we investigate a technique for grouping test runs that most likely reveal the same failure. This reduces the post analysis time and enables the generation of small regression test suites. The test case grouping is implemented by means of spectrum-based fault localization at the level of the specification. We calculate the grouping by relating the spectra of the test cases. Besides a brief discussion of our approach we present results of applying our approach to the Session Initiation Protocol.