testing-anti-patterns

Testing mock behavior means asserting on mock calls rather than actual component outcomes. Test the real code's behavior by verifying its output, state changes, or side effects, not whether the mock was invoked. This ensures tests catch real defects, not just mock configuration.

Test-only methods pollute production classes and violate separation of concerns. Instead, refactor production code into testable units, use dependency injection, or adjust test structure. Clean production code is easier to maintain and doesn't leak testing concerns into runtime logic.

Mocking without understanding dependencies creates tests that pass for wrong reasons—they test the mock's behavior, not the real dependency contract. Before mocking, understand what the dependency does, its inputs and outputs, and how your code uses it. This prevents brittle, misleading tests.

Effective unit tests verify real behavior, not mock existence. They fail when production code breaks, not when mocks change. Avoid asserting on mock state; instead verify your component's actual output, side effects, or error handling match expectations.

Refactor tests when they pass despite broken production code, rely heavily on mocks, or include test-only production methods. Use this skill when writing new tests or updating existing ones to ensure they catch real defects and remain maintainable as code evolves.