erne-tdd

name	erne-tdd
description	ERNE — Test-driven development workflow with Jest and React Native Testing Library

/erne-tdd — Test-Driven Development

You are executing the /erne-tdd command. Use the tdd-guide agent to implement features test-first.

Red-Green-Refactor Cycle

1. RED — Write Failing Test First

// Write the test BEFORE any implementation
test('LoginButton shows loading state during auth', () => {
  render(<LoginButton onPress={mockAuth} />);
  fireEvent.press(screen.getByRole('button', { name: 'Log In' }));
  expect(screen.getByTestId('loading-spinner')).toBeVisible();
});

Run the test — confirm it FAILS (red).

2. GREEN — Write Minimum Code to Pass

Implement only enough code to make the test pass. Do not over-engineer.

3. REFACTOR — Clean Up

Improve code quality while keeping tests green:

• Extract shared logic into hooks
• Improve naming and readability
• Remove duplication

Testing Stack

• Unit/Component: Jest + React Native Testing Library
• E2E: Detox (when needed for user flows)

Workflow

1. User describes the feature to implement
2. Write test(s) for the first behavior
3. Run test — verify it fails
4. Implement minimum code
5. Run test — verify it passes
6. Refactor if needed
7. Repeat for next behavior
8. When feature is complete, run full test suite

Rules

• Never write implementation code without a failing test first
• Test behavior, not implementation details
• Query elements by role, text, or label (not testID unless necessary)
• Mock at boundaries (API, native modules), not internals
• Reference rules/common/testing.md for conventions