You don't have to re-write this, it should be fine, it just seems like a good time to talk about testing philosophy (as I understand it). 

In the future try not to rely on internal implementation details/state. If you just test the larger behavior, even if it is more of an integration test, it allows you to change your source code and just re-run your tests to make sure that it all works. This is really one of the big advantages of having tests. If you're relying on your implementation in the tests, then you also have to re-write the tests when you change the code, defeating the purpose of the tests.

Tests can also act as a form of documentation, giving examples of the interactions with the code you are using. However, when you use the 'private' internal variables of the module, you are no longer demonstrating the desired behavior or how it is supposed to be used.

Again, not a big deal here, just something to keep in mind as you write future tests.