| name | testing-integration |
| description | Integration and E2E testing design. Use this when writing integration tests, E2E tests, or deciding what belongs in each test layer.
|
Skill: Integration & E2E Testing
Test Pyramid
/ E2E \ ← few: full system, real environment
/ Integr. \ ← moderate: real components, no network
/ Unit \ ← many: fast, isolated, mocked dependencies
- Unit tests — single function/class, mocked dependencies, milliseconds.
- Integration tests — two or more real components, no external network.
- E2E tests — compiled binary or deployed service, real user scenarios.
What Belongs in Integration Tests
- Two or more real components working together (no mocks at the boundary).
- Full pipeline execution with real files or data.
- Error propagation across component boundaries.
- File I/O, CLI flag parsing, or configuration loading.
Do NOT add integration tests for:
- Single-function logic — use a unit test.
- Flaky external network calls — stub or mock them.
E2E Test Design
An E2E test exercises the system exactly as a user would:
- Build/deploy the artifact once; reuse across test cases.
- Use real configuration, real files, real CLI arguments.
- Assert on user-visible output (stdout, files, HTTP responses).
- Clean up all side effects (temp files, test data).
Corner Cases for Integration & E2E
Before declaring a feature integration-tested, verify:
- Empty input — zero items, empty files.
- Malformed data — truncated files, wrong types.
- Large input — hundreds of items with deep nesting.
- Permission errors — unreadable or missing files.
- Concurrent execution — two workers processing the same data.
- Missing configuration — required env vars or config files absent.
Requirements → Tests Traceability
Every requirement should map to at least one test:
Requirement: "Users can export data as CSV"
├── Unit: TestCSVFormatter_ValidData_ReturnsCSV
├── Integration: TestExportPipeline_FetchAndFormat_ProducesFile
└── E2E: TestCLI_ExportCSV_WritesValidFile
If a requirement has no test, it is unverified. If a test maps to no
requirement, question whether it adds value.
