In testing, which statement accurately describes the role of mocks?

In testing, which statement accurately describes the role of mocks?

• A. A mock only provides canned responses
• B. A stub provides canned responses, while a mock verifies interactions
• C. A mock is used to verify interactions and expectations
• D. A mock has no use in unit testing

Answer: (C)

Mocks are about verifying how the unit under test interacts with its collaborators. You set expectations on the mock—such as which methods should be called, with which arguments, how many times, and in what order. When the test runs, the mock checks these expectations and the test fails if they aren’t met. This lets you confirm that the code under test uses its dependencies correctly. Mocks can also return controlled values to drive code paths, but the crucial part is the verification of interactions and expectations. In contrast, a stub mainly provides canned responses without monitoring usage. So, describing the role of mocks as verifying interactions and expectations captures their primary purpose.