testing-anti-patterns

Testing mock behavior instead of real component behavior creates false confidence in your tests. This anti-pattern occurs when assertions verify mock internals rather than actual component outputs. Write tests that exercise real dependencies and logic, using mocks only to isolate external concerns like API calls or databases, ensuring your tests validate genuine behavior.

Test-only methods in production code pollute your codebase and hide design issues. They couple production logic to testing needs and create maintenance burden. Instead, refactor code to be testable through its public API, use dependency injection to enable testing, or create separate test utilities outside production classes.

Use mocks to isolate the code under test from external dependencies like databases, APIs, or third-party services. Understand each dependency before mocking it—incomplete or incorrect mocks lead to tests that pass but code that fails in production. Mock only what's necessary; test real behavior of core logic and integration points.

Effective tests verify actual component behavior, not mock internals. Structure tests to exercise real logic paths, use complete mocks that accurately represent dependencies, and avoid test-only production code. Review tests during code review to catch anti-patterns like incomplete mocks or assertions on mock state rather than outcomes.

Testing implementation details means asserting on mock calls or internal state; testing behavior means verifying outputs and side effects. Behavior-focused tests remain valid when refactoring, while implementation-focused tests break unnecessarily. Focus assertions on what the code produces, not how it achieves it.