Testing path operations in FastAPI - Mini Project: Build & Apply

Testing path operations

📖 Scenario: You are building a simple web API using FastAPI. You want to make sure your API path operations work correctly by writing tests for them.

🎯 Goal: Create a FastAPI app with a path operation, then write a test using TestClient to check the path operation's response.

📋 What You'll Learn

Create a FastAPI app instance named app

Add a GET path operation at /hello that returns a JSON message

Create a test client instance named client using TestClient(app)

Write a test function named test_read_hello that sends a GET request to /hello and asserts the response status code is 200 and the JSON response matches the expected message

💡 Why This Matters

🌍 Real World

Testing path operations ensures your web API works correctly before deployment. It helps catch bugs early and improves reliability.

💼 Career

Writing tests for FastAPI path operations is a common task for backend developers and API engineers to maintain quality and confidence in their code.

1

Create FastAPI app and path operation

Create a FastAPI app instance called app. Add a GET path operation at /hello that returns the JSON {"message": "Hello, FastAPI!"}.

FastAPI

# Create FastAPI app and GET path operation at /hello
# Your code here

Need a hint?

Use FastAPI() to create the app. Use @app.get("/hello") decorator for the path operation. Return the exact JSON dictionary.

2

Import TestClient and create client instance

Import TestClient from fastapi.testclient. Create a test client instance called client using TestClient(app).

FastAPI

from fastapi import FastAPI

app = FastAPI()

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

# Import TestClient and create client instance
# Your code here

Need a hint?

Import TestClient from fastapi.testclient. Then create client = TestClient(app).

3

Write test function for GET /hello

Write a test function named test_read_hello. Inside it, use client.get("/hello") to send a GET request. Assert the response status code is 200 and the JSON response equals {"message": "Hello, FastAPI!"}.

FastAPI

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

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

client = TestClient(app)

# Write test function test_read_hello
# Your code here

Need a hint?

Define a function test_read_hello(). Use client.get("/hello") to get the response. Assert the status code and JSON content.

4

Complete test setup for running

Add the standard Python test check if __name__ == "__main__" block. Inside it, call test_read_hello() to run the test when the script is executed directly.

FastAPI

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()

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

client = TestClient(app)

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

# Add main check to run test_read_hello
# Your code here

Need a hint?

Add the block if __name__ == "__main__": and call test_read_hello() inside it.