17 Testing Httpx Pytest

title: Testing FastAPI with HTTPX and Pytest weight: 27 date: 2026-06-28 lastmod: 2026-06-28 description: Master FastAPI testing with TestClient (HTTPX), Pytest fixtures for database setup, dependency overrides, and comprehensive integration tests for all endpoints. tags: [api-development, fastapi]

Testing FastAPI uses TestClient from starlette.testclient (built on HTTPX) with Pytest fixtures for database setup, dependency overrides to mock auth, and test databases for isolated integration testing.

```python
# tests/conftest.py
import pytest
from fastapi.testclient import TestClient
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from app.main import app
from app.database import Base, get_db
from app import models

SQLALCHEMY_DATABASE_URL = "sqlite:///./test.db"
engine = create_engine(SQLALCHEMY_DATABASE_URL)
TestingSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

def override_get_db():
    db = TestingSessionLocal()
    try:
        yield db
    finally:
        db.close()

app.dependency_overrides[get_db] = override_get_db

@pytest.fixture(autouse=True)
def setup_database():
    Base.metadata.create_all(bind=engine)
    yield
    Base.metadata.drop_all(bind=engine)

@pytest.fixture
def client():
    return TestClient(app)

@pytest.fixture
def test_user(client):
    response = client.post("/api/users", json={
        "username": "testuser",
        "email": "test@test.com",
        "password": "Test1234!"
    })
    return response.json()

# tests/test_users.py
def test_create_user(client):
    response = client.post("/api/users", json={
        "username": "alice",
        "email": "alice@test.com",
        "password": "SecurePass1!"
    })
    assert response.status_code == 201
    assert response.json()["username"] == "alice"

def test_get_user_not_found(client):
    response = client.get("/api/users/999")
    assert response.status_code == 404

What's Next

Now learn about WebSocket support in Building REST APIs with FastAPI.