Introduction: Test Doubles—Stubs and Mocks

In this section, we’re going to solve a common testing challenge.

How do you test an object that depends on another object? What do we do if that collaborator is difficult to set up with test data?

Several techniques are available to help us with this and they build on the SOLID principles we learned previously. We can use the idea of dependency injection to enable us to replace collaborating objects with ones specially written to help us write our test.