Starting FastAPI Tests

Writing effective tests is crucial for ensuring the quality and reliability of your FastAPI applications. In this section, we’ll explore the fundamental concepts of testing FastAPI applications using Pytest. We’ll cover topics like creating test clients, testing endpoints, and handling database interactions.

Creating a Test Client

To test your FastAPI application, you’ll need to create a test client using the TestClient class from the fastapi.testclient module. This client allows you to make HTTP requests to your application and inspect the responses.

Example:

Python

import pytest
from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

@app.get("/")
def read_root():
    return {"Hello": "World"}

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

In this example, we create a TestClient instance within a fixture named client. This allows us to use the client in our test functions.

Testing Endpoints

Once you have a test client, you can use it to make requests to your application’s endpoints and assert the expected results.

Example:

Python

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

In this example, we test the / endpoint by making a GET request and asserting that the response status code is 200 and the response JSON contains the expected data.

Testing Database Interactions

If your FastAPI application interacts with a database, you’ll need to handle database setup and teardown in your tests. You can use fixtures or custom code to manage database connections and data.

Example:

Python

@pytest.fixture
def db_session():
    # Create a database session
    session = Session()
    yield session
    session.close()

def test_create_user(client, db_session):
    # Create a user
    response = client.post("/users", json={"name": "Alice"})
    assert response.status_code == 201

    # Check if the user was created
    user = db_session.query(User).filter(User.name == "Alice").first()
    assert user is not None

In this example, we create a db_session fixture to manage the database session. We use the fixture to create a user and then check if the user was created successfully.