Node.js — Testing

Jest

npm install -D jest

Basic Test

// sum.test.js
function sum(a, b) {
    return a + b;
}

test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
});

Test Suite

describe('Calculator', () => {
    test('adds numbers', () => {
        expect(add(1, 2)).toBe(3);
    });
    
    test('subtracts numbers', () => {
        expect(subtract(5, 3)).toBe(2);
    });
});

Matchers

Matcher	Description
toBe	Strict equality
toEqual	Deep equality
toBeTruthy	Is truthy
toContain	Array contains
toThrow	Throws error
toBeNull	Is null

Async Tests

test('fetches data', async () => {
    const data = await fetchData();
    expect(data).toBeDefined();
});

Mocking

jest.mock('./database');

test('calls database', async () => {
    const mockFn = jest.fn().mockResolvedValue({ id: 1 });
    const result = await mockFn();
    expect(result).toEqual({ id: 1 });
});

Run Tests

npm test
npx jest --coverage
npx jest --watch

Mini Practice

1. Write basic tests
2. Create test suites
3. Use different matchers
4. Mock functions

Up Next

Continue with Security — security best practices.