testing-anti-patterns

Testing mock behavior verifies the mock exists, not that your application works. Instead, test real behavior by asserting on actual outputs and side effects. Mock only external dependencies, then verify your code's genuine logic through functional assertions.

Test-only methods pollute production code, create maintenance debt, and expose internal details that shouldn't exist. Write tests against the public API instead. If you need special test hooks, reconsider your design—TDD naturally prevents this by requiring testable, clean interfaces first.

Common anti-patterns include testing mock existence, incomplete mocks that hide real failures, over-mocking that decouples tests from actual behavior, and test-only production code. This Skill identifies these patterns with concrete examples and provides fixes to ensure tests genuinely verify application behavior.

TDD enforces writing tests before code, naturally preventing test-only methods and over-mocking. You design for testability upfront, mock only what's necessary, and avoid testing implementation details. This discipline produces robust, maintainable tests that verify real behavior.

Review tests against the 3 Iron Laws: each test should verify one behavior, use mocks only for external dependencies, and assert on real outcomes—not mock calls. Apply gate functions before asserting on mocks, adding production methods, or completing mocks to catch anti-patterns early.

Yes, mocking frameworks are valuable when used correctly. Mock only external dependencies (APIs, databases, services), not the code under test. Verify real behavior through assertions on actual outputs, not mock interactions. Understand your dependencies before mocking to avoid false confidence.