test-coverage-improver

Test Coverage Improver

Instructions

When improving test coverage:

1. Run coverage report to identify gaps
2. Prioritize critical/complex code paths
3. Write tests for uncovered code
4. Verify coverage improved

Generate Coverage Report

# Jest
npx jest --coverage

# Vitest
npx vitest --coverage

# NYC (Istanbul) for any test runner
npx nyc npm test

# View HTML report
open coverage/lcov-report/index.html

Coverage Targets

Type	Minimum	Good	Excellent
Lines	70%	80%	90%+
Branches	60%	75%	85%+
Functions	70%	80%	90%+
Statements	70%	80%	90%+

Test Templates

Unit Test (Jest/Vitest)

import { describe, it, expect, vi, beforeEach } from 'vitest';
import { calculateTotal, formatCurrency } from './utils';

describe('calculateTotal', () => {
  it('should sum all item prices', () => {
    const items = [
      { price: 10, quantity: 2 },
      { price: 5, quantity: 1 },
    ];
    expect(calculateTotal(items)).toBe(25);
  });

  it('should return 0 for empty array', () => {
    expect(calculateTotal([])).toBe(0);
  });

  it('should handle decimal prices', () => {
    const items = [{ price: 10.99, quantity: 1 }];
    expect(calculateTotal(items)).toBeCloseTo(10.99);
  });
});

Testing Async Functions

describe('fetchUser', () => {
  it('should return user data', async () => {
    const user = await fetchUser(1);
    expect(user).toEqual({
      id: 1,
      name: expect.any(String),
      email: expect.stringContaining('@'),
    });
  });

  it('should throw for non-existent user', async () => {
    await expect(fetchUser(999)).rejects.toThrow('User not found');
  });
});

Mocking Dependencies

import { vi } from 'vitest';
import { sendEmail } from './email';
import { createUser } from './user';

vi.mock('./email', () => ({
  sendEmail: vi.fn().mockResolvedValue({ success: true }),
}));

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

  it('should send welcome email after creating user', async () => {
    await createUser({ name: 'John', email: '[email protected]' });

    expect(sendEmail).toHaveBeenCalledWith({
      to: '[email protected]',
      template: 'welcome',
    });
  });
});