testing-anti-patterns

Unit tests pass but miss real bugs when they verify mock behavior instead of actual functionality. This common testing anti-pattern occurs when mocks are configured without understanding dependencies, causing tests to validate the mock setup rather than the real code behavior.

A test-only method is production code added solely to support unit tests, which pollutes the codebase. Avoid this testing anti-pattern by using Test-Driven Development (TDD) to design testable interfaces naturally, preventing the need for test-specific logic in production.

You should mock a dependency only after ensuring a proper understanding of its actual behavior. Mocking without this understanding leads to testing mock behavior rather than real functionality, creating unreliable unit tests that fail to validate actual code paths.

TDD prevents testing anti-patterns by driving code design through tests first, ensuring you test real behavior rather than mock implementations. This approach naturally eliminates the need for test-only methods in production code and clarifies dependency boundaries before mocking.

The best way to ensure unit tests verify real behavior is to focus tests on actual functionality rather than mock implementations. Use gate functions at critical decision points during test development to validate that dependencies are understood before mocking.

You should not use mocking when you lack a proper understanding of the dependency's real behavior. Mocking without this understanding leads to testing anti-patterns where tests validate the mock setup rather than the actual code, resulting in false confidence during refactoring.