trezor-suite/skills/tests-common.md

Writing Common Tests (TDD)

This skill enforces Test-Driven Development (TDD) practices for suite-common packages and ensures proper usage of the @suite-common/test-utils package.

Core Principles

1. Test-First Development

• ALWAYS write tests before implementing features in suite-common packages.
• Follow the Red-Green-Refactor cycle:
  1. Red: Write a failing test that describes the desired behavior. Run test to confirm it fails for the right reason (e.g., "Expected value to be X but got Y").
  2. Green: Write the minimum code to make the test pass. Run test to confirm it passes.
  3. Refactor: Clean up the code while keeping tests green. Run test to confirm it still passes after refactoring.

2. Writing tests

• Focus on testing behavior and user interactions, not implementation details.
• Follow arrange-act-assert pattern for test structure.

3. Use @suite-common/test-utils Package

• REQUIRED: Use @suite-common/test-utils for all suite-common testing that involves React hooks.
• NEVER import directly from @testing-library/react when testing hooks.
• The test-utils package provides all necessary utilities including renderHookWithStoreProvider.

Checklist

Before submitting code, ensure:

• Tests were written BEFORE implementation
• Using @suite-common/test-utils for hook tests (not direct @testing-library/react)
• Correct render function used (renderHookWithStoreProvider for hooks needing store, renderHook otherwise)
• Fixtures are properly typed
• Tests focus on behavior, not implementation
• Tests follow naming conventions (.hook.test.ts, .test.ts)
• All tests pass locally