Testing Standards

Rule: Test real behavior, not mock behavior. Never pollute production code with test-only methods.

When to use this skill

When writing new test files or test cases in any testing framework (Jest, Vitest, pytest, RSpec, Go testing, JUnit)
When modifying existing tests that use mocks, stubs, spies, or test doubles
When considering whether to add a method or property to a production class that would only be used in tests
When test setup involves creating mock objects or configuring mock behavior
When deciding between testing with real dependencies versus mocked dependencies
When tests are failing and you need to determine if the issue is in the code or in how mocks are configured
When implementing fixtures, test data builders, or test utilities
During test code reviews to ensure testing best practices are followed
When test files contain assertions that check for mock existence (e.g., expect(screen.getByTestId('component-mock')))
When refactoring production code and tests need to be updated accordingly
When choosing isolation strategies for unit tests versus integration tests