Creating of unit tests of a method with 1 bool parameter needs at least 2 unit tests (false and true). But how many unit tests do you need for a parameter of type IEnumerable? A variant of the Permutations() method will help you to create almost all necessary combinations with just one extension method!
A long story today, but very instructive if you do not have much experience with SOLID. I will give you 2 clues in advance: