Comparing mocks, stubs, and spies in unit tests

We’ll spend this section comparing mocks, stubs, and spies in unit tests because they’re essential tools for isolating and simulating components’ behaviors during testing. Understanding their differences will help us choose the right approach to test various interactions and functionalities in the system effectively.

Mocks

A mock is a simulated object that replaces a real dependency in a unit test. It’s designed to mimic the behavior of the original object but with complete control over its actions. Why? This isolation allows for focused testing of the code under scrutiny without the need to rely on external factors.

We can define exact return values, exceptions, or sequences of actions for mock objects. This enables us to test various scenarios and edge cases. Mocks can record interactions, allowing us to verify that methods were called with correct arguments, in the right order, and with the expected...