FastAPI – Testing API with pytest #10

In this tutorial, we will be learning how to test an API built with FastAPI using pytest. FastAPI is a modern web framework for building APIs with Python that is fast, easy to use, and efficient. Pytest is a testing framework that makes it easy to write simple and scalable tests in Python.

Before we begin, make sure you have FastAPI and pytest installed. You can install them using pip:

pip install fastapi pytest

Create a new Python file called main.py and add the following code:

from fastapi import FastAPI

app = FastAPI()

@app.get("/hello")
async def hello():
    return {"message": "Hello, World!"}

This code creates a simple FastAPI application with one endpoint /hello that returns a JSON response with a message "Hello, World!".

Now, create a new Python file called test_main.py and add the following code:

from fastapi.testclient import TestClient
from main import app

client = TestClient(app)

def test_hello():
    response = client.get("/hello")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello, World!"}

This code imports the TestClient class from fastapi.testclient and our FastAPI application app from main.py. We then create a test function test_hello() that sends a GET request to the /hello endpoint using the client and asserts that the response status code is 200 and the response JSON matches the expected message.

To run the tests, open a terminal and run the following command:

pytest test_main.py

You should see the output that indicates that the test passed successfully.

This is a basic example of testing a FastAPI API using pytest. You can write more test functions to cover different endpoints and scenarios. FastAPI provides several features to make testing APIs easy and efficient, such as dependency injection, automatic validation, and automatic documentation generation.

In conclusion, testing APIs is an essential part of building reliable and robust applications. By using FastAPI and pytest, you can write tests that are easy to understand, maintain, and execute, ensuring the quality and stability of your API.