testing-integration

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:

1. Build/deploy the artifact once; reuse across test cases.
2. Use real configuration, real files, real CLI arguments.
3. Assert on user-visible output (stdout, files, HTTP responses).
4. 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.