Write tests that verify individual functions in isolation. Use assertions: expect(actual).toBe(expected).

• Tests that verify individual functions in isolation

function add(a, b) { return a + b; }
function subtract(a, b) { return a - b; }

describe('Math functions', () => {
  describe('add', () => {
    it('adds two numbers', () => {
// ...

• Unit tests demonstrate test structure

• Test one thing per test; use clear names: 'should handle edge case'
• Arrange, Act, Assert: set up, call function, check result
• Test both happy path and edge cases: 0, null, empty, negative

Write tests that verify individual functions in isolation. Use assertions: expect(actual).toBe(expected).

• Tests that verify individual functions in isolation

function add(a, b) { return a + b; }
function subtract(a, b) { return a - b; }

describe('Math functions', () => {
  describe('add', () => {
    it('adds two numbers', () => {
// ...

• Unit tests demonstrate test structure

• Test one thing per test; use clear names: 'should handle edge case'
• Arrange, Act, Assert: set up, call function, check result
• Test both happy path and edge cases: 0, null, empty, negative