Testing-Anti-Patterns

Testing mock behavior defeats the purpose of unit tests. Focus assertions on actual component outputs and side effects, not on whether mocks were called or exist. Verify real behavior by testing against actual dependencies or minimal stubs that preserve essential interactions.

Test-only methods pollute production code, obscure real APIs, and create maintenance burden. Keep production classes clean by testing through public interfaces only. If you need special test hooks, reconsider your test design or use dependency injection instead.

Mock only external dependencies—APIs, databases, file systems—where you need to isolate behavior or control side effects. Never mock the code under test. Understand what each dependency does before mocking it; mocking without that knowledge leads to tests that pass but hide real bugs.

Tests should assert on observable outcomes—return values, state changes, side effects—not internal mock calls or test-specific conditions. Write complete, behavior-focused tests that would catch actual breakage in production, not just changes to how mocks are configured.

Common anti-patterns include testing mock existence, adding test-only methods to production, over-mocking without understanding dependencies, and testing implementation instead of behavior. These weaken confidence in tests and leak test concerns into production code.

During maintenance, remove test-only methods, replace unnecessary mocks with real implementations or minimal stubs, and ensure assertions target actual behavior. Refactor tests to stay focused on verifiable outcomes, applying the Iron Laws consistently as code evolves.