Introducing the 12 Factors for Good Tests

Most tests suck.
Yours might too.

Learn how to fix them with the 12 Factors methodology and real examples of what NOT to do.

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The 12 Factors for Good Tests

A methodology for building test suites that are fast, reliable, and actually useful.

Isolation

Tests are hermits

Clarity

Test names are documentation

Speed

Fast tests get run, slow tests get skipped

Determinism

Flaky tests are worse than no tests

Focus

One test, one concern

Portability

No 'works on my machine'

Resilience

Tests adapt to refactoring

Maintenance

Delete bad tests ruthlessly

Boundaries

Mock the edges, not the core

Data

Test data tells a story

Diagnostics

Failures should scream what's wrong

Depth

Coverage ≠ quality

Explore All 12 Factors

Get a taste of the horror

Testing Implementation, Not Behavior

😱 This Will Haunt Your CI

// 😱 BAD: Testing internal implementation
test('user service', () => {
  const userService = new UserService();
  const spy = jest.spyOn(userService, 'validateEmail');
  
  userService.createUser('john@example.com', 'password');
  
  expect(spy).toHaveBeenCalledWith('john@example.com');
  expect(userService.users.length).toBe(1);
});

✅ Actually Useful Test

// ✅ GOOD: Testing behavior and outcomes
test('creates user with valid email', async () => {
  const result = await createUser('john@example.com', 'password');
  
  expect(result.success).toBe(true);
  expect(result.user.email).toBe('john@example.com');
  
  const user = await findUserByEmail('john@example.com');
  expect(user).toBeDefined();
});

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Most tests suck.Yours might too.