Toolkit Fastapi Unit Tester

from fastapi.testclient import TestClient
from app.main import app

client = TestClient(app)

def test_create_item_success():
    response = client.post("/items/", json={"name": "widget", "price": 9.99})
    assert response.status_code == 201
    assert response.json()["name"] == "widget"

def test_create_item_missing_field():
    response = client.post("/items/", json={"price": 9.99})
    assert response.status_code == 422

Rules

• Mock external I/O (DB, HTTP clients, file system) — unit tests must not hit real services.
• Use app.dependency_overrides to swap FastAPI dependencies in tests.
• Avoid testing Pydantic model validation in route tests; test models separately.
• Assert both status code and relevant response body fields.
• Keep each test focused on one scenario — no multi-assertion "God tests".

Examples

• "Write unit tests for the POST /users/ endpoint."
• "Generate test cases for this FastAPI route including auth failure scenarios."
• "Review these endpoint tests for coverage gaps."