MockedValues

Mocked values are placeholders used in unit tests to simulate the output of external dependencies or complex objects. They allow a test to focus on the unit under test by providing controllable inputs and expected outputs without requiring the real implementation. This technique is common in test frameworks such as Mockito for Java, unittest.mock for Python, and jest.mock for JavaScript.

When a function calls another component—such as a database, web service, or calculation module—a mocked value can replace the actual return value. The test defines the behavior of the mock (e.g., return 42, raise an exception, or record that a method was called) and then verifies that the unit responds correctly. For example, a service method that calculates shipping cost may mock the price lookup to return a fixed price, ensuring that the shipping calculation logic is exercised independently of the price service.

Best practice recommends keeping mocks simple: use stubs for predictably returning values and mocks for verifying interactions. Over‑mocking can make tests brittle and obscure real faults. When a dependency becomes part of the public API, tests should check both the mocked path and the real path by re‑enabling the actual implementation for integration tests.

Common pitfalls include not resetting mock state between tests, leading to cross‑test contamination, and mocking too many methods, which can hide missing responsibilities in the unit. A balanced approach is to mock only what is necessary for isolation, keeping tests fast, readable and maintainable.