api-testing

API Testing

Test backend APIs using pytest + httpx (integration) or FastAPI TestClient (unit). Write tests to /tmp, execute via python.

Decision Tree

API to test → Is it a FastAPI app?
    ├─ Yes → Use TestClient (no server needed)
    │         from fastapi.testclient import TestClient
    │
    └─ No → Use httpx (server must be running)
             import httpx

FastAPI TestClient (Unit Tests)

# /tmp/test_api.py
import pytest
from fastapi.testclient import TestClient
from server import app  # Import your FastAPI app

client = TestClient(app)

def test_health():
    r = client.get("/health")
    assert r.status_code == 200

def test_create_item():
    r = client.post("/items", json={"name": "test", "price": 9.99})
    assert r.status_code == 201
    data = r.json()
    assert data["name"] == "test"
    assert "id" in data

def test_auth_required():
    r = client.get("/protected")
    assert r.status_code == 401

def test_with_auth():
    r = client.get("/protected", headers={"Authorization": "Bearer test-token"})
    assert r.status_code == 200

httpx (Integration Tests)

# /tmp/test_integration.py
import httpx
import pytest

BASE_URL = "http://localhost:8000"  # Adjust to target

def test_endpoint_responds():
    r = httpx.get(f"{BASE_URL}/health")
    assert r.status_code == 200

def test_crud_flow():
    # Create
    r = httpx.post(f"{BASE_URL}/items", json={"name": "test"})
    assert r.status_code == 201
    item_id = r.json()["id"]

    # Read
    r = httpx.get(f"{BASE_URL}/items/{item_id}")
    assert r.status_code == 200

    # Delete
    r = httpx.delete(f"{BASE_URL}/items/{item_id}")
    assert r.status_code == 204

Execution

# Run all tests
cd <project_dir> && python -m pytest /tmp/test_api.py -v

# Run with coverage
cd <project_dir> && python -m pytest /tmp/test_api.py --cov=. --cov-report=term

Testing Patterns

Pattern	When	Example
Happy path	Always first	POST /items → 201
Error scenarios	Required	Invalid input → 422, Not found → 404
Auth flows	If protected	No token → 401, Bad token → 403
Edge cases	Important	Empty body, large payload, special chars
Contract validation	API changes	Verify response schema matches spec