yanacuti1121/yana-ai/ai-regression-testing

1. Error state leakage — happy path tested, error path returns wrong data
2. Missing rollback — DB write succeeds, second step fails, no rollback
3. SELECT clause omissions — query returns partial data silently
4. Sandbox/production path divergence — works in test, breaks with real env vars
5. Auth check on create but not update/delete — classic AI shortcut
6. Off-by-one in pagination — AI copies the pattern, gets limits wrong
7. Unhandled null from optional fields — AI trusts the type, skips null guard

Bug found in /api/user/profile
        ↓
Write a test that FAILS with the bug present
        ↓
Verify the test actually fails (run it now)
        ↓
Apply the fix
        ↓
Verify test now passes
        ↓
Commit test + fix together

// vitest.config.ts — force sandbox mode for all tests
export default defineConfig({
  test: {
    env: { NODE_ENV: 'test', SANDBOX_MODE: '1' },
    setupFiles: ['./tests/setup.ts'],
  },
})
// tests/setup.ts
process.env.DATABASE_URL = undefined  // no real DB
process.env.SANDBOX_MODE = '1'

// Bug: /api/user/profile returned 200 with empty object when user not found
describe('GET /api/user/profile regression', () => {
  it('returns 404 when user does not exist', async () => {
    const res = await request(app)
      .get('/api/user/profile')
      .set('Authorization', 'Bearer valid-but-unknown-user-token')
    expect(res.status).toBe(404)        // was 200 before fix
    expect(res.body.id).toBeUndefined() // was {} before fix
  })
})

❌ Writing the test after the fix (test may never have caught the bug)
❌ Test that passes before AND after the fix (proves nothing)
❌ Sandboxed test that never hits the actual auth/DB path the bug was in
❌ "We trust the AI won't make that mistake again" — it will
✅ Run test with bug present → confirm FAIL → apply fix → confirm PASS
✅ Tag regression tests: describe('[regression] bug description', ...)