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  && python -m pytest /tmp/test_api.py -v

# Run with coverage
cd  && 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 |

Response Schema Validation

def test_response_schema():
    r = client.get("/items/1")
    data = r.json()
    # Verify required fields exist
    assert "id" in data
    assert "name" in data
    assert isinstance(data["id"], int)
    assert isinstance(data["name"], str)

Mocking External Dependencies

from unittest.mock import patch, AsyncMock

def test_with_mocked_service():
    with patch("services.external_api.fetch_data", new_callable=AsyncMock) as mock:
        mock.return_value = {"status": "ok"}
        r = client.get("/dashboard")
        assert r.status_code == 200
        mock.assert_called_once()

Anti-Patterns

| ❌ Don't | ✅ Do | |----------|-------| | Test against production | Use TestClient or local server | | Hardcode auth tokens | Use fixtures or env vars | | Skip error scenarios | Test 4xx/5xx responses explicitly | | Ignore response body | Validate schema + data |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: omnigentx
• Source: omnigentx/jarvis
• License: MIT

Install and usage instructions live in the source repository linked above.