| name | integration-e2e-testing |
| description | Designs integration and E2E tests with mock boundaries and behavior verification rules. Use when writing E2E or integration tests. |
Integration Test & E2E Test Design/Implementation Rules
References
Test Types and Limits
| Test Type | Purpose | Scope | External Deps | File Format | Limit per Feature | Implementation Timing |
|---|
| Integration | Verify component interactions in-process | Partial system integration (in-process modules; for UI components, RTL+MSW for React/TS) | Mocked or in-process | *.int.test.ts | MAX 3 | Created alongside implementation |
| fixture-e2e | Verify UI behavior in a browser with deterministic fixtures | Full UI flow with mocked backend / fixture-driven state | Mocked / fixture only — no live services | *.fixture-e2e.test.ts | MAX 3 | Created alongside the UI feature |
| service-integration-e2e | Verify critical user journeys against a running local stack | Full system across services | Live local services or stubs | *.service-e2e.test.ts | MAX 1-2 | Executed only in the final phase |
Lane selection (E2E only):
- Default lane for user-facing UI journeys is fixture-e2e — it runs a real browser against deterministic fixtures, catches the bugs that unit/integration tests miss (button no-op, state never updates, navigation breaks), and runs in CI without infrastructure setup
- Add service-integration-e2e only when the journey's correctness depends on real cross-service behavior (data persistence, transactional consistency, external service contracts) that cannot be faked safely
The two E2E lanes are budgeted independently — having a fixture-e2e for a journey does not consume the service-integration-e2e budget and vice versa.
Critical User Journey: Features with revenue impact, legal requirements, or daily use by majority of users
Behavior-First Principle
Observability Check (All YES = Include)
| Check | Question | If NO |
|---|
| Observable | Can user observe the result? | Exclude |
| System Context | Does it require integration of multiple components? | Exclude |
| Automatable | Can it run stably in CI environment? | Exclude |
Include/Exclude Criteria
Include: Business logic accuracy, data integrity, user-visible features, error handling
Exclude: External live connections, performance metrics, implementation details, UI layout
Skeleton Specification
Required Comment Format
The committed skeleton imports only the test framework (for describe/it/it.todo); the module under test is imported by the implementing task, never by the skeleton — a skeleton that references a not-yet-created module can fail gates that type-check, compile, or load test files before implementation begins.
Each test MUST include the following annotations.
@lane selection rule:
integration — Component interaction in-process, no browser (e.g., RTL+MSW for React/TS, in-process module/handler integration in any language)fixture-e2e — Browser-level UI verification with mocked backend / fixture-driven state. @dependency is typically full-ui (mocked backend)service-integration-e2e — Browser-level or end-to-end verification against running local services or stubs. @dependency is full-system
Property Annotations
Multi-Step User Journey Definition
A feature qualifies as containing a multi-step user journey when ALL of the following are true:
- 2+ distinct interaction boundaries are traversed in sequence to complete a user goal. What counts as a boundary depends on the system type:
- Web: distinct routes/pages
- Mobile native: distinct screens/views
- CLI: distinct command invocations or interactive prompts
- API: distinct API calls forming a transaction (e.g., create → confirm → finalize)
- State carries across steps — data produced or actions taken in one step affect what the next step accepts or displays
- The journey has a completion point — a final state the user or caller reaches (e.g., confirmation page, saved record, API success response, completed workflow)
User-Facing vs Service-Internal Journeys
Multi-step journeys are classified for reserved-slot eligibility:
| Classification | Condition | Reserved Slot Eligibility | Example |
|---|
| User-facing | A human user directly triggers and observes the steps (via UI, CLI, or direct API interaction) | Eligible — defaults to fixture-e2e reserved slot. Add a service-integration-e2e reserved slot only when the journey's correctness depends on real cross-service behavior | Web checkout flow, CLI setup wizard, mobile onboarding |
| Service-internal | Steps are triggered by backend services without direct user interaction | Not eligible for reserved slot — use integration tests. service-integration-e2e through normal ROI > 50 path is still valid when full-system verification is warranted | Async job pipeline, service-to-service saga, scheduled batch processing |
This classification applies to the reserved-slot rule and the E2E Gap Check. Other selection follows lane-specific ROI rules below.
ROI Calculation
ROI is used to rank candidates within the same test type (integration candidates against each other, E2E candidates against each other). Cross-type comparison is unnecessary because integration and E2E budgets are selected independently.
ROI Score = Business Value × User Frequency + Legal Requirement × 10 + Defect Detection
(range: 0–120)
Higher ROI Score = higher priority within its test type. No normalization or capping is applied — the raw score is used directly for ranking. Deduplication is a separate step that removes candidates entirely; it does not modify scores.
ROI Thresholds by Lane
The two E2E lanes have very different ownership costs and use independent thresholds.
| Lane | ROI threshold | Rationale |
|---|
| fixture-e2e | ROI ≥ 20 (beyond reserved slot) | Cost is comparable to integration tests once the harness exists; the floor avoids filling MAX 3 with low-signal tests when fewer would suffice |
| service-integration-e2e | ROI > 50 (beyond reserved slot) | Creation, execution, and maintenance cost is 3-10× higher than integration; reserve for journeys whose value cannot be proven any other way |
Reserved slot rules apply per lane and override the threshold (the reserved candidate is emitted regardless of its ROI score). Below-floor candidates beyond the reserved slot are not emitted, leaving budget intentionally unfilled rather than padding with low-value tests.
ROI Calculation Examples
| Scenario | BV | Freq | Legal | Defect | ROI Score | Test Type | Selection Outcome |
|---|
| Core checkout UI flow | 10 | 9 | true | 9 | 109 | fixture-e2e | Selected (reserved slot: user-facing multi-step journey, browser verification with fixtures) |
| Core checkout against live payment service | 10 | 9 | true | 9 | 109 | service-integration-e2e | Selected (real-service correctness above ROI threshold) |
| Dismiss button updates UI state | 6 | 7 | false | 8 | 50 | fixture-e2e | Selected (rank 2 of 3 fixture-e2e budget) |
| Payment error message display (UI) | 5 | 4 | false | 7 | 27 | fixture-e2e | Selected (rank 3 of 3 fixture-e2e budget) |
| Optional filter toggle | 3 | 4 | false | 2 | 14 | fixture-e2e | Not selected (rank 4, budget full) |
| Payment retry against real provider | 8 | 3 | false | 7 | 31 | service-integration-e2e | Below ROI threshold (31 < 50), not selected |
| DB persistence check | 8 | 8 | false | 8 | 72 | Integration | Selected (rank 1 of 3) |
| Pure data transformation | 5 | 3 | false | 4 | 19 | Integration | Selected (rank 2 of 3) |
Implementation Rules
Property-Based Test Implementation
When Property annotation exists, fast-check library is required:
import fc from 'fast-check'
it('AC2-property: Model name is always gemini-3-pro-image-preview', () => {
fc.assert(
fc.property(fc.string(), (prompt) => {
const result = client.generate(prompt)
return result.model === 'gemini-3-pro-image-preview'
})
)
})
Requirements:
- Write in
fc.assert(fc.property(...)) format
- Reflect skeleton's
// fast-check: comment directly in implementation
- When failure case discovered, add as concrete unit test (regression prevention)
Behavior Verification Implementation
Behavior Description Verification Levels:
| Step Type | Verification Target | Example |
|---|
| Trigger | Reproduce in Arrange | API failure -> mockResolvedValue({ ok: false }) |
| Process | Intermediate state or call | Function call, state change |
| Observable Result | Final output value | Return value, error message, log output |
Pass Criteria: Pass if "observable result" is verified as return value or mock call argument of test target
Verification Item Determination Rules
| Skeleton State | Verification Item Determination Method |
|---|
// Verification items: listed | Implement all listed items with expect |
No // Verification items: | Derive from "observable result" in "Behavior" description |
| Both present | Prioritize verification items, use behavior as supplement |
Integration Test Mock Boundaries
| Judgment Criteria | Mock | Actual |
|---|
| Part of test target? | No -> Can mock | Yes -> Actual required |
| Is call verification target of test? | No -> Can mock | Yes -> Actual or verifiable mock |
| External network communication? | Yes -> Mock required | No -> Actual recommended |
Judgment Flow:
- External API (HTTP communication) -> Mock required
- Component interaction under test -> Actual required
- Log output verification needed -> Use verifiable mock (vi.fn())
- Log output verification not needed -> Actual or ignore
E2E Test Execution Conditions
fixture-e2e:
- Execute alongside the UI feature implementation phase (not deferred to the end)
- Use mocked backend / fixture-driven state (
@dependency: full-ui (mocked backend)); no live services required
- Runs in CI without infrastructure setup
service-integration-e2e:
- Execute only in the final phase, after all components are implemented and the local stack is up
- Use real local services or service stubs — no in-process mocks for the components under verification (
@dependency: full-system)
Review Criteria
Skeleton and Implementation Consistency
| Check | Failure Condition |
|---|
| Property Verification | Property annotation exists but fast-check not used |
| Behavior Verification | No expect for "observable result" |
| Verification Item Coverage | Listed verification items not included in expect |
| Mock Boundary | Internal components mocked in integration test |
Implementation Quality
| Check | Failure Condition |
|---|
| AAA Structure | Arrange/Act/Assert separation unclear |
| Independence | State sharing between tests, execution order dependency |
| Reproducibility | Depends on date/random, results vary |
| Readability | Test name and verification content don't match |
