Fixture organization in FastAPI - Mini Project: Build & Apply

Fixture Organization in FastAPI Testing

📖 Scenario: You are building a simple FastAPI app that manages a list of books. You want to write tests that use fixtures to organize your test data and setup.

🎯 Goal: Create and organize fixtures in FastAPI tests using pytest to provide test data and a test client.

📋 What You'll Learn

Create a fixture for a list of books with exact entries

Create a fixture for a FastAPI test client

Use the fixtures in a test function to check the number of books

Organize fixtures properly for reuse in tests

💡 Why This Matters

🌍 Real World

Organizing fixtures helps keep tests clean and reusable when building APIs with FastAPI.

💼 Career

Understanding fixture organization is essential for writing maintainable automated tests in professional FastAPI projects.

1

Create a fixture with a list of books

Create a fixture function called books that returns a list of dictionaries with these exact entries: {'id': 1, 'title': '1984'}, {'id': 2, 'title': 'Brave New World'}, and {'id': 3, 'title': 'Fahrenheit 451'}. Use the @pytest.fixture decorator.

FastAPI

import pytest

# Create a fixture called books that returns the list of book dictionaries
# Your code here

Need a hint?

Use @pytest.fixture above a function named books that returns the list.

2

Create a fixture for the FastAPI test client

Import FastAPI and TestClient from fastapi and fastapi.testclient. Create a fixture called client that creates a FastAPI app instance and returns a TestClient for it. Use the @pytest.fixture decorator.

FastAPI

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

@pytest.fixture
def books():
    return [
        {'id': 1, 'title': '1984'},
        {'id': 2, 'title': 'Brave New World'},
        {'id': 3, 'title': 'Fahrenheit 451'}
    ]

# Create a fixture called client that returns a TestClient for a FastAPI app
# Your code here

Need a hint?

Import FastAPI and TestClient. Define client fixture that returns TestClient(app).

3

Write a test function using the fixtures

Write a test function called test_books_count that takes books as a parameter. Inside, assert that the length of books is exactly 3.

FastAPI

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

@pytest.fixture
def books():
    return [
        {'id': 1, 'title': '1984'},
        {'id': 2, 'title': 'Brave New World'},
        {'id': 3, 'title': 'Fahrenheit 451'}
    ]

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

# Write a test function test_books_count that takes books and asserts len(books) == 3
# Your code here

Need a hint?

Define test_books_count with books parameter and assert length is 3.

4

Add a route to use the fixtures in the app

Add a GET route /books to the FastAPI app inside the client fixture that returns the books list. Modify the client fixture to accept books as a parameter and use it in the route. This completes the fixture organization for testing.

FastAPI

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

@pytest.fixture
def books():
    return [
        {'id': 1, 'title': '1984'},
        {'id': 2, 'title': 'Brave New World'},
        {'id': 3, 'title': 'Fahrenheit 451'}
    ]

@pytest.fixture
def client(books):
    app = FastAPI()
    # Add a GET /books route that returns books
    # Your code here
    return TestClient(app)

def test_books_count(books):
    assert len(books) == 3

Need a hint?

Modify client fixture to accept books, add @app.get('/books') route returning books.