JavaScript Testing Patterns

Comprehensive testing patterns for modern JavaScript/TypeScript applications.

Core Principle: AAA Pattern

Every test follows Arrange, Act, Assert:

test('calculates total with discount', () => {
  // Arrange - Set up test data
  const cart = { items: [{ price: 100 }], discount: 0.1 }

  // Act - Execute the code under test
  const total = calculateTotal(cart)

  // Assert - Verify the result
  expect(total).toBe(90)
})