Every Release Breaks Something: Zero Tests in AI Code

The problem

A SaaS platform was experiencing critical production failures with every deployment. Their release notes read like horror stories: "v2.3.1 - Fixed login bug introduced in v2.3.0", "v2.3.2 - Restored deleted user data from v2.3.1 fix". The team spent 60% of their time on emergency hotfixes. Customer churn hit 23% as users lost faith in the platform's stability. The codebase had 47,000 lines of code and exactly zero automated tests.

How AI created this issue

The startup had built their entire MVP using AI code generation. When developers asked for tests, here's what happened:

// Developer: "Write tests for this user service"
// AI Response:
describe('UserService', () => {
  it('should work correctly', () => {
    // TODO: Add test implementation
    expect(true).toBe(true);
  });
});

// Developer: "Write actual tests please"
// AI Response:
describe('UserService', () => {
  it('creates a user', () => {
    const user = createUser('test@example.com');
    expect(user).toBeDefined();
  });
});

The AI consistently generated shallow, meaningless tests that provided zero actual coverage. It never tested error cases, edge conditions, or integration points. Developers got frustrated and skipped testing entirely, assuming they'd "add tests later" (which never happened). The AI also never suggested setting up CI/CD pipelines or test infrastructure.

The solution

1. Test coverage analysis: Used coverage tools to identify the riskiest untested code paths
2. Critical path testing first: Started with authentication, payments, and data persistence:

   
   // Proper integration test with edge cases
   describe('Authentication Flow', () => {
     let testDb;
     
     beforeEach(async () => {
       testDb = await createTestDatabase();
     });
     
     afterEach(async () => {
       await testDb.cleanup();
     });
     
     describe('User Login', () => {
       it('successfully authenticates valid credentials', async () => {
         const user = await testDb.createUser({
           email: 'test@example.com',
           password: 'SecurePass123!'
         });
         
         const response = await request(app)
           .post('/api/auth/login')
           .send({ email: 'test@example.com', password: 'SecurePass123!' });
         
         expect(response.status).toBe(200);
         expect(response.body.token).toBeDefined();
         expect(response.body.user.id).toBe(user.id);
       });
       
       it('rejects invalid password with proper error', async () => {
         await testDb.createUser({
           email: 'test@example.com',
           password: 'SecurePass123!'
         });
         
         const response = await request(app)
           .post('/api/auth/login')
           .send({ email: 'test@example.com', password: 'WrongPassword' });
         
         expect(response.status).toBe(401);
         expect(response.body.error).toBe('Invalid credentials');
         expect(response.body.token).toBeUndefined();
       });
       
       it('handles database connection failures gracefully', async () => {
         await testDb.disconnect();
         
         const response = await request(app)
           .post('/api/auth/login')
           .send({ email: 'test@example.com', password: 'any' });
         
         expect(response.status).toBe(503);
         expect(response.body.error).toBe('Service temporarily unavailable');
       });
     });
   });

3. CI/CD pipeline with test gates: No code merges without passing tests and 80% coverage
4. Regression test automation: Every bug fix required a test to prevent recurrence
5. End-to-end testing: Implemented Playwright tests for critical user journeys
6. Performance regression tests: Added k6 load tests to catch performance degradations

The results

• Production incidents dropped 94% (from 12/month to 0.7/month)
• Deployment frequency increased 4x with confidence
• Customer churn reduced to 4.2% as stability improved
• Developer productivity up 40% - less time firefighting
• Code coverage reached 87% for critical paths
• Mean time to recovery (MTTR) improved from 4 hours to 23 minutes

The team learned that AI-generated code without tests is technical debt in disguise. They now require tests for all new features and use AI to help write tests only after manually defining test scenarios. Their new motto: "If it's not tested, it's broken."