cause-and-effect

Problem: 15% of test runs fail, passing on retry

PEOPLE
├─ Test-writing skills vary across team
├─ New developers copy existing flaky patterns
└─ No one assigned to fix flaky tests

PROCESS
├─ Flaky tests marked as "known issue" and ignored
├─ No policy against merging with flaky tests
└─ Test failures don't block deployments

TECHNOLOGY
├─ Race conditions in async test setup
├─ Tests share global state
├─ Test database not isolated per test
├─ setTimeout used instead of proper waiting
└─ CI environment inconsistent (different CPU/memory)

ENVIRONMENT
├─ CI runner under heavy load
├─ Network timing varies (external API mocks flaky)
└─ Timezone differences between local and CI

METHODS
├─ Integration tests not properly isolated
├─ No retry logic for legitimate timing issues
└─ Tests depend on execution order

MATERIALS
├─ Test data fixtures overlap
├─ Shared test database polluted
└─ Mock data doesn't match production patterns

ROOT CAUSES:
- No test isolation strategy (Methods + Technology)
- Process accepts flaky tests (Process)
- Async timing not handled properly (Technology)

SOLUTIONS:
1. Implement per-test database isolation (high impact)
2. Replace setTimeout with proper async/await patterns (medium impact)
3. Add pre-commit hook blocking flaky test patterns (prevents new issues)
4. Enforce policy: flaky test = block merge (process change)

Problem: Simple CRUD feature took 12 weeks vs. 3 week estimate

PEOPLE
├─ Developer unfamiliar with codebase
├─ Key architect on vacation during critical phase
└─ Designer changed requirements mid-development

PROCESS
├─ Requirements not finalized before starting
├─ No code review for first 6 weeks (large diff)
├─ Multiple rounds of design revision
└─ QA started late (found issues in week 10)

TECHNOLOGY
├─ Codebase has high coupling (change ripple effects)
├─ No automated tests (manual testing slow)
├─ Legacy code required refactoring first
└─ Development environment setup took 2 weeks

ENVIRONMENT
├─ Staging environment broken for 3 weeks
├─ Production data needed for testing (compliance delay)
└─ Dependencies blocked by another team

METHODS
├─ No incremental delivery (big bang approach)
├─ Over-engineering (added future features "while we're at it")
└─ No design doc (discovered issues during implementation)

MATERIALS
├─ Third-party API changed during development
├─ Production data model different than staging
└─ Missing design assets (waited for designer)

ROOT CAUSES:
- No requirements lock-down before start (Process)
- Architecture prevents incremental changes (Technology)
- Big bang approach vs. iterative (Methods)
- Development environment not automated (Technology)

SOLUTIONS:
1. Require design doc + finalized requirements before starting (Process)
2. Implement feature flags for incremental delivery (Methods)
3. Automate dev environment setup (Technology)
4. Refactor high-coupling areas (Technology, long-term)