erne-tdd
ERNE — Test-driven development workflow with Jest and React Native Testing Library
About this skill
This AI agent skill, `/erne-tdd`, provides a structured guide for implementing features in a Test-Driven Development (TDD) manner. It explicitly directs the AI agent to follow the classic Red-Green-Refactor cycle: first writing a failing test, then implementing the minimum code to make that test pass, and finally refactoring for code quality and readability without breaking tests. The skill outlines explicit steps, workflow, and rules, ensuring a disciplined test-first approach is maintained. The primary use case involves developing new features for React Native or Expo applications, ensuring each piece of functionality is covered by automated tests. By enforcing a TDD workflow, this skill helps the AI agent produce robust, reliable code with high test coverage, reducing the likelihood of bugs and improving maintainability. It serves as a comprehensive instruction set for the AI to emulate a disciplined human developer's TDD process, leveraging Jest and React Native Testing Library for unit and component tests.
Best use case
The primary use case is for AI agents assisting human developers in building new features for React Native/Expo applications, strictly following a TDD approach. It's ideal for developers who want to leverage AI for coding tasks while maintaining high code quality, comprehensive test coverage, and a disciplined development process, particularly for critical application logic or UI components.
ERNE — Test-driven development workflow with Jest and React Native Testing Library
The user should expect well-tested, maintainable React Native code for new features, developed rigorously following the Red-Green-Refactor cycle.
Practical example
Example input
Use `/erne-tdd` to implement a new user authentication flow: a secure login form that validates email and password, shows a loading state, and redirects on successful login.
Example output
Okay, I'll start by writing a failing test for the email validation in the login form.
```tsx
// src/components/LoginForm/LoginForm.test.tsx
import { render, screen, fireEvent } from '@testing-library/react-native';
import LoginForm from './LoginForm';
test('LoginForm displays error for invalid email', () => {
render(<LoginForm onSubmit={jest.fn()} />);
fireEvent.changeText(screen.getByPlaceholderText('Email'), 'invalid-email');
fireEvent.press(screen.getByRole('button', { name: 'Login' }));
expect(screen.getByText('Invalid email format')).toBeVisible();
});
```
This test should fail initially. Then I will write the minimum code to make it pass, following the Red-Green-Refactor cycle for each behavior.When to use this skill
- When implementing new features or functionality in a React Native or Expo project.
- To ensure high test coverage and robust code quality for new development.
- When a disciplined, test-first development approach is required.
- For developing components or logic where reliability and maintainability are paramount.
When not to use this skill
- For quick bug fixes in existing code that do not involve new features or behavioral changes.
- When rapid prototyping without immediate test coverage is prioritized.
- If the project does not utilize Jest or React Native Testing Library for testing.
- For purely exploratory coding or significant refactoring that doesn't add new behavior.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/erne-tdd/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How erne-tdd Compares
| Feature / Agent | erne-tdd | Standard Approach |
|---|---|---|
| Platform Support | Claude | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | easy | N/A |
Frequently Asked Questions
What does this skill do?
ERNE — Test-driven development workflow with Jest and React Native Testing Library
Which AI agents support this skill?
This skill is designed for Claude.
How difficult is it to install?
The installation complexity is rated as easy. You can find the installation instructions above.
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
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SKILL.md Source
# /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
```tsx
// 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 conventionsRelated Skills
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