How to set up pytest and TestClient for FastAPI testing

Testing Setup with pytest and TestClient

FastAPI's TestClient wraps httpx to send HTTP requests to your app without starting a real server. It is synchronous regardless of whether your routes are async.

Install

pip install pytest httpx

Basic test

# tests/test_main.py
from fastapi.testclient import TestClient
from app.main import app

client = TestClient(app)

def test_read_root():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello, FastAPI"}

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

conftest.py for shared fixtures

# tests/conftest.py
import pytest
from fastapi.testclient import TestClient
from app.main import app

@pytest.fixture
def client():
    with TestClient(app) as c:
        yield c

Using the context manager form of TestClient triggers FastAPI's startup and shutdown events, which is required when your app registers event handlers. Put shared fixtures in conftest.py — pytest discovers them automatically without import.

Running tests

pytest -v
pytest tests/test_main.py::test_read_root  # single test