Skills/test-generator

test-generator

Name: test-generator
Author: terminal-skills

Generate unit, integration, and end-to-end tests for existing code. Use when a user asks to write tests, add test coverage, create unit tests, generate integration tests, build e2e tests, improve code coverage, write specs, or add testing to a project. Supports Jest, Vitest, Pytest, Playwright, React Testing Library, and Cypress. Analyzes code to produce meaningful assertions, edge cases, and mock setups.

#testing#unit-tests#e2e#jest#pytest

terminal-skillsv1.0.0

Works with:claude-codeopenai-codexgemini-clicursor

Source

Usage

✓ Installed test-generator v1.0.0

Getting Started

Install the skill using the command above
Open your AI coding agent (Claude Code, Codex, Gemini CLI, or Cursor)
Reference the skill in your prompt
The AI will use the skill's capabilities automatically

Example Prompts

"Review the open pull requests and summarize what needs attention"
"Generate a changelog from the last 20 commits on the main branch"

Documentation

Overview

Automatically generate comprehensive tests for existing source code. This skill analyzes functions, classes, and modules to produce well-structured test suites with meaningful assertions, edge case coverage, and proper mocking. It supports multiple frameworks and test types (unit, integration, e2e).

Instructions

When a user asks you to generate tests for their code, follow these steps:

Step 1: Analyze the target code

Read the source file(s) and identify:

Functions/methods to test, their signatures, parameters, and return types
Dependencies that need mocking (database calls, API requests, file I/O)
Edge cases — null inputs, empty arrays, boundary values, error paths
Side effects — state mutations, event emissions, DOM changes

Step 2: Detect the testing framework

Check the project for existing test setup:

bash

# Check package.json for JS/TS projects
cat package.json | grep -E "jest|vitest|playwright|cypress|mocha|testing-library"

# Check for Python test frameworks
cat requirements.txt pyproject.toml setup.cfg 2>/dev/null | grep -E "pytest|unittest|hypothesis"

# Check for existing test config
ls jest.config* vitest.config* pytest.ini conftest.py .pytest.ini setup.cfg 2>/dev/null

If no framework is detected, recommend based on the project:

React/Next.js: Vitest + React Testing Library
Node.js/Express: Jest or Vitest
Python: Pytest
E2E/browser: Playwright

Step 3: Generate the test file

Create tests following the framework conventions:

Naming: Place test files next to source files or in a __tests__/tests directory matching the project convention. Use *.test.ts, *.spec.ts, test_*.py, or *_test.py.

Structure each test with:

Arrange — set up inputs, mocks, and preconditions
Act — call the function or perform the action
Assert — verify the output, side effects, or state changes

For each function, generate tests covering:

Happy path with typical inputs
Edge cases (empty input, null, zero, max values)
Error handling (invalid input, thrown exceptions)
Boundary conditions

Step 4: Set up mocks and fixtures

Mock external dependencies to isolate the unit under test:

JavaScript/TypeScript (Jest/Vitest):

typescript

import { describe, it, expect, vi, beforeEach } from 'vitest';
import { processOrder } from './order-service';
import { db } from './database';
import { sendEmail } from './email-service';

vi.mock('./database');
vi.mock('./email-service');

describe('processOrder', () => {
  beforeEach(() => {
    vi.clearAllMocks();
  });

  it('should save the order and send confirmation email', async () => {
    const mockOrder = { id: 'ord_123', items: [{ sku: 'WIDGET-A', qty: 2 }], total: 49.98 };
    vi.mocked(db.orders.create).mockResolvedValue(mockOrder);
    vi.mocked(sendEmail).mockResolvedValue({ delivered: true });

    const result = await processOrder({ items: [{ sku: 'WIDGET-A', qty: 2 }] });

    expect(db.orders.create).toHaveBeenCalledOnce();
    expect(sendEmail).toHaveBeenCalledWith(expect.objectContaining({ orderId: 'ord_123' }));
    expect(result.id).toBe('ord_123');
  });
});

Python (Pytest):

python

import pytest
from unittest.mock import patch, MagicMock
from order_service import process_order

@pytest.fixture
def mock_db():
    with patch('order_service.db') as mock:
        mock.orders.create.return_value = {"id": "ord_123", "total": 49.98}
        yield mock

def test_process_order_saves_and_sends_email(mock_db):
    result = process_order(items=[{"sku": "WIDGET-A", "qty": 2}])
    mock_db.orders.create.assert_called_once()
    assert result["id"] == "ord_123"

def test_process_order_rejects_empty_items():
    with pytest.raises(ValueError, match="at least one item"):
        process_order(items=[])

Step 5: Add integration and e2e tests if requested

Integration tests — test multiple modules together with real (or test) databases:

Use test containers or in-memory databases
Test API routes end-to-end through the HTTP layer
Verify database state after operations

E2E tests (Playwright):

typescript

import { test, expect } from '@playwright/test';

test('user can add item to cart and checkout', async ({ page }) => {
  await page.goto('/products');
  await page.click('[data-testid="product-widget-a"]');
  await page.click('button:has-text("Add to Cart")');

  await page.goto('/cart');
  await expect(page.locator('.cart-item')).toHaveCount(1);
  await expect(page.locator('.cart-total')).toContainText('$24.99');

  await page.click('button:has-text("Checkout")');
  await expect(page).toHaveURL(/\/checkout/);
});

Step 6: Verify and report coverage

Run the tests and report results:

bash

# JavaScript
npx vitest run --coverage
# Python
pytest --cov=src --cov-report=term-missing

Report: total tests, pass/fail, and coverage percentage. Suggest additional tests if coverage is below 80%.

Examples

Example 1: Generate unit tests for a utility module

User request: "Write tests for src/utils/string-helpers.ts"

Source code analyzed:

typescript

export function slugify(text: string): string {
  return text.toLowerCase().replace(/\s+/g, '-').replace(/[^a-z0-9-]/g, '');
}
export function truncate(text: string, maxLength: number): string {
  if (text.length <= maxLength) return text;
  return text.slice(0, maxLength - 3) + '...';
}

Generated test file (src/utils/string-helpers.test.ts):

typescript

import { describe, it, expect } from 'vitest';
import { slugify, truncate } from './string-helpers';

describe('slugify', () => {
  it('converts spaces to hyphens', () => {
    expect(slugify('Hello World')).toBe('hello-world');
  });
  it('removes special characters', () => {
    expect(slugify('Price: $99.99!')).toBe('price-9999');
  });
  it('handles empty string', () => {
    expect(slugify('')).toBe('');
  });
  it('collapses multiple spaces', () => {
    expect(slugify('too   many   spaces')).toBe('too-many-spaces');
  });
});

describe('truncate', () => {
  it('returns original if within limit', () => {
    expect(truncate('short', 10)).toBe('short');
  });
  it('truncates and adds ellipsis', () => {
    expect(truncate('This is a very long sentence', 15)).toBe('This is a ve...');
  });
  it('handles exact length', () => {
    expect(truncate('exact', 5)).toBe('exact');
  });
});

Result: 7 tests generated, all passing. Coverage: 100% for string-helpers.ts.

Example 2: Generate Pytest tests for a Flask API endpoint

User request: "Add tests for the /api/users endpoint in app.py"

Source code analyzed:

python

@app.route('/api/users', methods=['POST'])
def create_user():
    data = request.get_json()
    if not data.get('email'):
        return jsonify({"error": "Email is required"}), 400
    user = User(email=data['email'], name=data.get('name', ''))
    db.session.add(user)
    db.session.commit()
    return jsonify({"id": user.id, "email": user.email}), 201

Generated test file (tests/test_users_api.py):

python

import pytest
from app import app, db

@pytest.fixture
def client():
    app.config['TESTING'] = True
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
    with app.test_client() as client:
        with app.app_context():
            db.create_all()
        yield client

def test_create_user_success(client):
    response = client.post('/api/users', json={"email": "alice@example.com", "name": "Alice"})
    assert response.status_code == 201
    data = response.get_json()
    assert data["email"] == "alice@example.com"
    assert "id" in data

def test_create_user_missing_email(client):
    response = client.post('/api/users', json={"name": "Bob"})
    assert response.status_code == 400
    assert "Email is required" in response.get_json()["error"]

def test_create_user_empty_body(client):
    response = client.post('/api/users', json={})
    assert response.status_code == 400

Result: 3 tests generated, all passing. Covers success, validation error, and empty input.

Guidelines

Always match the existing test framework and style in the project. Do not introduce Jest if the project uses Vitest.
Place test files following the project's existing convention (co-located vs. tests/ directory).
Use descriptive test names that explain the expected behavior, not the implementation.
Mock external dependencies (databases, APIs, file system) but avoid over-mocking — test real logic.
For each function, aim for at least: one happy path, one error case, one edge case.
Generate beforeEach/afterEach setup when tests share common fixtures.
Do not generate snapshot tests unless explicitly requested — they are brittle and rarely useful.
When generating e2e tests, use stable selectors (data-testid) over CSS classes.
If the project has no testing setup, install the framework and create the config file before writing tests.
Report test count and coverage after generation so the user knows the current state.