Unit testing a method that calls another method

testingunit testing

What is the best way to unit test a method that calls into multiple methods, for example:

modify(string value)
    if(value.Length > 5)  replaceit(value);

    else changeit(value);

This pseudo code has a modify method that (currently) calls either replaceit() or changeit(). I have already wrote tests for replaceit and changeit, so writing a new test for modify will be 99% the same set of code. I need to test it thought because it may change in the future.

So do I copy paste the existing test code? Move the test code to a common function? Any other ideas? I'm not sure of the best practice here.

Best Answer

This is a classic state-based test vs. behavior-based test scenario.

In this ridiculously simple example testing the output is fine. At some point though, you'll run into tests where inspecting the state after execution is complicated. Instead you want to check the behavior (e.g. verify that changeit was called with a specific value).

At that point you probably should look into a mock object framework like Rhino.Mocks (.Net) or Mockito (Java) and start writing more interface based code.