testing-anti-patterns

Testing Anti-Patterns

You are identifying and avoiding common testing anti-patterns.

Review Workflow

Follow these steps when reviewing test code:

1. Run tests in isolation — Verify each test passes independently (no shared state, no ordering dependency).
2. Check for patterns below — Scan for each anti-pattern in the checklist; flag every match with the specific defect.
3. Apply refactoring strategy — Use the refactoring strategies section to select and apply the appropriate fix.
4. Verify the test still fails when code breaks — After fixing, confirm the corrected test catches real regressions (remove or stub the implementation to confirm a failure occurs).

Critical Anti-Patterns

1. The Liar - Tests That Always Pass

Problem: Test passes even when the code is broken.

// BAD - Always passes because it tests nothing meaningful
it('should process data', () => {
  const result = processData(input);
  expect(result).toBeDefined(); // Too weak
});

// GOOD - Actually verifies behavior
it('should transform input to uppercase', () => {
  const result = processData({ text: 'hello' });
  expect(result.text).toBe('HELLO');
});

Detection: Remove or break the implementation - test should fail.

2. The Giant - Tests Too Large

Problem: Single test covers too many behaviors.

// BAD - Tests multiple things
it('should handle user registration', async () => {
  const user = await register(userData);
  expect(user.id).toBeDefined();
  expect(user.email).toBe(userData.email);
  expect(user.password).toBeUndefined();
  expect(sendEmail).toHaveBeenCalled();
  expect(createProfile).toHaveBeenCalled();
  // ... 20 more assertions
});

// GOOD - Focused tests
it('should create user with provided email', async () => {
  const user = await register(userData);
  expect(user.email).toBe(userData.email);
});

it('should send welcome email on registration', async () => {
  await register(userData);
  expect(sendEmail).toHaveBeenCalledWith(
    expect.objectContaining({ type: 'welcome' })
  );
});