# Fastapi Integration Test Pattern > Procedure for writing integration tests for FastAPI endpoints, covering dependency overriding and mock coordinator setup. Use when this capability is needed. - Skill: `tomevault-io/fastapi-integration-test-pattern` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/fastapi-integration-test-pattern` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/fastapi-integration-test-pattern/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Integrations & APIs - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/fastapi-integration-test-pattern --- ## When to Use Use when creating new integration tests for FastAPI endpoints within the T1D Companion codebase to ensure consistency and proper setup of the authentication and service-coordinator stack. ## Procedure 1. **Mount Target Router**: Ensure the target router is mounted on a fresh `FastAPI()` instance. 2. **Dependency Overrides**: Use `app.dependency_overrides` to inject patched versions of `get_db`, `require_active_user`, and `get_current_user`. 3. **Mock Coordinator**: Attach a mock coordinator instance to `app.state.coordinator` to bypass production service chains. 4. **Test Client**: Use `Starlette.testclient.TestClient` for synchronous HTTP calls. 5. **Async/Sync Verification**: Mark test functions with `@pytest.mark.asyncio` for any async database or service logic assertions. 6. **Teardown**: Always include a fixture or finalizer to clear `app.dependency_overrides` after each test to prevent state pollution. ## Pitfalls * **Pollution**: Not resetting `app.dependency_overrides` makes tests flaky and dependent on execution order. * **Initialization**: Omitting the mock coordinator in `app.state` almost always causes runtime errors in the Service layer. ## Verification Refer to `tests/test_chat_integration.py` and `tests/test_api_auth.py` for canonical implementations. --- > Source: [ruskibeats/t1d](https://github.com/ruskibeats/t1d) — distributed by [TomeVault](https://tomevault.io).