public void assertFiltersMutationAtNLocations(int n, Sample s, GregorMutater mutator) { final List<MutationDetails> mutations = mutator.findMutations(s.className); final Collection<MutationDetails> actual = filter(s.clazz, mutations, mutator); final Set<Loc> originalLocations = new LinkedHashSet<>(); FCollection.mapTo(mutations, toLocation(s.clazz), originalLocations); final Set<Loc> filteredLocations = new LinkedHashSet<>(); FCollection.mapTo(actual, toLocation(s.clazz), filteredLocations); assertThat(filteredLocations) .describedAs("Expected to filter %d locations from the %d in %s", n, originalLocations.size(), s.clazz.toString()) .hasSize(originalLocations.size() - n); }