Only testing public methods
TDD is all about testing the behaviors of components, not their implementations. As we have seen in our test in the previous section, having a test for the behavior we want enables us to choose any implementation that will do the job. We focus on what’s important – what a component does – not on the less important details – how it does it.
Inside a test, this appears as calling public methods or functions on public classes and packages. The public methods are the behaviors we choose to expose to the wider application. Any private data or supporting code in classes, methods, or functions remain hidden.
A common mistake that developers make when learning TDD is that they make things public just to simplify testing. Resist the temptation. A typical mistake here is to take a private data field and expose it for testing using a public getter method. This weakens the encapsulation of that class. It is now more likely that the...
