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09 — Testing

Test your API with pytest — auth, RBAC, and CRUD.

What you'll learn

  • pytest basics for FastAPI
  • TestClient for HTTP requests
  • Fixtures for database and auth tokens
  • What each test file covers

THEORY

Why test APIs?

  • Catch bugs before deployment
  • Document expected behavior
  • Safe to refactor when tests pass

Test stack

Tool Purpose
pytest Test runner
TestClient Simulates HTTP requests without running server
In-memory SQLite Fresh DB per test — no pollution

Test structure

tests/
├── conftest.py           # Shared fixtures (DB, tokens, client)
└── api/v1/
    ├── test_auth.py      # Register, login, refresh
    ├── test_rbac.py      # Admin vs user permissions
    └── test_tasks.py     # CRUD + ownership

conftest.py explained

Key fixtures:

Fixture Purpose
client TestClient for HTTP calls
setup_database Creates tables + seed users (autouse)
user_token JWT for regular user
admin_token JWT for admin
auth_headers {"Authorization": "Bearer ..."}

DB override:

app.dependency_overrides[get_db] = override_get_db

Tests use in-memory SQLite instead of real task_api.db.

Running tests

make test
# or
pytest tests/ -v
pytest tests/api/v1/test_auth.py -v   # single file

PRACTICE

1. Run all tests

cd backend-with-fastapi/task-api
source .venv/bin/activate
make test

Expected: 15 passed

2. Read one test

Open tests/api/v1/test_auth.py → test_register_and_login — follow the flow.

3. Break something on purpose

Change TaskService.create_task to always raise an error — run tests — see which fail — fix it.

4. Write a new test (exercise)

Add to test_tasks.py:

def test_create_task_requires_title(client, auth_headers):
    response = client.post(
        "/api/v1/tasks",
        json={"title": "", "status": "pending"},
        headers=auth_headers,
    )
    assert response.status_code == 422

Run: pytest tests/api/v1/test_tasks.py::test_create_task_requires_title -v

Test coverage map

Test file Covers
test_auth.py Register, login, refresh, /me, duplicate email
test_rbac.py Admin list users, user denied, admin sees all tasks
test_tasks.py CRUD, pagination, auth required, ownership 403
health/ready DB connectivity

Common mistakes

Mistake Fix
Tests hit real database Use dependency override + in-memory DB
Rate limit breaks tests limiter.enabled = False in conftest
Forgetting auth headers Use auth_headers fixture

Next

→ 10 — Docker & Deployment