While your given "quirk" is true (TIMTOWTDI and all), I draw exactly the opposite conclusion from it: When there are many ways to do something, the philosophical side helps to decide which is the appropriate way in any given situation.

More relevantly to the original question, being likely to change the implementation of a method over the lifetime of the code means that it's less of an issue if your testing code mirrors the (original) implementation, since it will still assure you that the method produces the same results after its implementation is changed. (But, that said, I agree with earlier responses that this particular case sounds like one in which breaking the code down further into finer-grained methods and testing those smaller pieces independently is the way to go.)