Integration Test & E2E Test Design/Implementation Rules

References

• references/e2e-design.md - E2E test design principles with Playwright (candidate properties, selection criteria, candidate record)
• references/e2e-environment-prerequisites.md - service-integration-e2e environment prerequisites (seed data, auth fixtures, environment checklist); fixture-e2e requires no live service or real database

Test Types and Selection

Test Type	Purpose	Scope	External Deps	File Format	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	Created alongside implementation
fixture-e2e	Verify browser behavior with deterministic fixtures	Full UI flow with mocked backend / fixture-driven state	Mocked / fixture only — no live services	*.fixture-e2e.test.ts	Created alongside the UI feature
service-integration-e2e	Verify a contract that only a running stack can expose	Full system across services	Live local services or service-level stubs	*.service-e2e.test.ts	Executed after the required services exist

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
• Select service-integration-e2e when the proof obligation is real cross-service behavior such as data persistence, transactional consistency, or an external service contract

Start from accepted proof obligations, assign each to the cheapest boundary that can expose its failure, remove duplicate coverage, and keep the smallest set that covers every remaining distinct failure. Let those obligations determine the test count. A feature may validly produce no test in a lane.

Behavior-First Principle

Candidate Evidence

An integration/E2E candidate states:

• an observable result at the boundary named by the accepted behavior
• a material failure that crosses the components exercised by the selected lane
• an automated harness or controlled environment capable of reproducing that failure

Route behavior observable in isolation to unit/component verification. Record an unavailable controlled environment as a proof prerequisite for service-integration-e2e.

Candidate Routing

• Keep business-logic accuracy, data integrity, user-visible behavior, and observable error handling in the integration/E2E pool when they require those boundaries
• Route pure implementation details and data transformations to unit tests, performance claims to performance verification, and layout-only claims to visual or UI checks
• Represent external contracts with service-level stubs or a controlled local service when that contract is the proof target

Skeleton Specification

Required Skeleton Format

A committed file matching the project's test include pattern must remain valid to its runner. Use the detected framework's smallest pending suite (describe plus it.todo, or its equivalent), with only the test-framework import and the required comments. The implementing task replaces pending cases and adds application imports, assertions, fixtures, and mock setup alongside implementation.

Each test MUST include the following annotations.

// AC: "[Acceptance criteria original text]"
// Behavior: [Trigger] -> [Process] -> [Observable Result]
// @lane: integration | fixture-e2e | service-integration-e2e
// @dependency: none | [component names] | full-ui (mocked backend) | full-system
// @real-dependency: [component name] (optional, when Test Boundaries specify non-mock setup)
// Primary failure mode: [specific regression that must make the implemented test fail]
// Proof obligation: [boundary and observable state the implemented test must assert]
// Verification items: [observations that establish the obligation]

@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

// Property: `[Verification expression]`
// fast-check: fc.property(fc.[arbitrary], (input) => [invariant])

Test Set Selection

1. Read the accepted behavior and each recorded proof obligation from the governing artifact or task.
2. For each obligation, name the material failure that must make a test fail and the observable state that exposes it.
3. Search existing tests. Reuse coverage only when it exercises the same boundary and would fail for that failure.
4. Assign the obligation to the narrowest sufficient lane:
   • unit/component when isolated execution exposes the behavior
   • integration for in-process component contracts
   • fixture-e2e for browser behavior whose backend may be deterministic
   • service-integration-e2e for persistence, transactions, messages, or external contracts whose failure is exposed only through that running boundary
5. Merge obligations when one scenario proves them while preserving a clear assertion-to-failure mapping. Keep distinct setup and failure modes in separate scenarios.
6. Emit only the remaining minimal covering set. Record the accepted behavior, primary failure, proof obligation, selected lane, and mock boundary in each skeleton.

Select from accepted behavior and repository proof boundaries; product analytics and numerical value estimates are unnecessary. Escalate when the accepted behavior or required contract remains unresolved after consulting governing sources and repository evidence.

Implementation Rules

Property-Based Test Implementation

When a Property annotation exists, fast-check is required:

• 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

Take the first row that matches the claim under review:

Condition	Boundary to use
The external adapter, query, migration, or service contract itself is under test	The real boundary, or a service-level stub in the service-integration-e2e lane — a mock cannot prove the contract it stands in for
External API or network call not under test	Mock
Component interaction under test	Real in-process components
The call itself is what the test verifies (e.g., log output)	A verifiable mock (vi.fn())
Neither the call nor its target is under test	Real, or ignore

E2E Test Execution Conditions

fixture-e2e:

• Execute alongside the UI feature implementation phase
• Use mocked backend / fixture-driven state (@dependency: full-ui (mocked backend))
• Run in CI with the deterministic fixture setup

service-integration-e2e:

• Execute only in the final phase, after all components are implemented and the local stack is up
• Exercise components under verification through real local services or service-level stubs (@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

Route Parity for Shared Mutations

When multiple routes reach the same mutation — a CLI path and an HTTP handler, a scheduled job and a manual trigger, a batch and a single-item endpoint — compare them along four axes: validation, classification, resource bounds, and the order of read, parse, mutation, and reporting.

A difference is permitted only by a source that decides intent: a requirement, the Design Doc, or an ADR. Tests sit downstream of that decision — they record the behavior that exists, so an existing test covering the permissive route confirms the bypass rather than permitting it. Once a difference is permitted, a test verifies that it behaves as decided.

When a difference has no permitting source, require a test that exposes the bypass: drive the mutation through the route that skips the check and assert the state the skipped check was protecting.

Check	Failure Condition
Validation parity	One route validates an input the other accepts unchecked, with no requirement or contract permitting the difference
Classification parity	The same failure is classified differently per route, changing what the caller observes
Resource-bound parity	One route enforces a size, count, or timeout bound the other omits
Operation-order parity	Routes differ in read/parse/mutation/reporting order such that one can mutate before validating or report before persisting
Bypass coverage	An unexplained difference has no test driving the mutation through the permissive route