Tech & Engineering/8 min read

Unit Testing Best Practices: Writing Tests That Actually Matter

Artiphishle|January 15, 2026

testingbest-practicesjavascript

Writing good tests is an art form. Here's what I've learned after years of testing production code.

The AAA Pattern

The Arrange-Act-Assert pattern is your foundation:

1describe(class="text-category-music">'calculateTotal', () => {
2  it(class="text-category-music">'should apply discount correctly', () => {
3    // Arrange
4    class="text-category-tech font-medium">const items = [{ price: 100 }, { price: 50 }]
5    class="text-category-tech font-medium">const discount = 0.1
6
7    // Act
8    class="text-category-tech font-medium">const result = calculateTotal(items, discount)
9
10    // Assert
11    expect(result).toBe(135)
12  })
13})

Test Behavior, Not Implementation

Don't test how something works, test what it does:

1// Bad: Testing implementation
2it(class="text-category-music">'should call sort class="text-category-tech font-medium">function', () => {
3  class="text-category-tech font-medium">const spy = jest.spyOn(array, class="text-category-music">'sort')
4  sortUsers(users)
5  expect(spy).toHaveBeenCalled()
6})
7
8// Good: Testing behavior
9it(class="text-category-music">'should class="text-category-tech font-medium">return users sorted by name', () => {
10  class="text-category-tech font-medium">const result = sortUsers([{ name: class="text-category-music">'Zoe' }, { name: class="text-category-music">'Alice' }])
11  expect(result[0].name).toBe(class="text-category-music">'Alice')
12})

Keep Tests Independent

Each test should be able to run in isolation. Avoid shared state that can cause flaky tests.