Why testing ensures reliability in FastAPI - See It in Action

Why testing ensures reliability

📖 Scenario: You are building a simple FastAPI application that manages a list of tasks. To make sure your app works correctly and reliably, you will write tests that check the main features.

🎯 Goal: Create a FastAPI app with a list of tasks, add a configuration for a minimum task length, implement a route to add tasks only if they meet the length requirement, and write a test to verify this behavior.

📋 What You'll Learn

Create a list called tasks with initial tasks

Add a variable MIN_TASK_LENGTH to set the minimum allowed length for a task

Write a POST route /add-task that adds a task only if it meets the minimum length

Write a test function using TestClient to check that short tasks are rejected and valid tasks are added

💡 Why This Matters

🌍 Real World

Testing ensures that your web app works correctly every time you change code. This prevents bugs from reaching users and keeps your app reliable.

💼 Career

Writing tests is a key skill for software developers. It shows you can build stable, maintainable applications that companies trust.

1

DATA SETUP: Create the initial tasks list

Create a list called tasks with these exact string entries: 'buy milk', 'read book', and 'write code'.

FastAPI

# Create the tasks list with initial tasks
# Your code here

Need a hint?

Use a Python list with the exact task strings inside square brackets.

2

CONFIGURATION: Add minimum task length variable

Add a variable called MIN_TASK_LENGTH and set it to the integer 5.

FastAPI

from fastapi import FastAPI

app = FastAPI()

tasks = ['buy milk', 'read book', 'write code']

# Set minimum task length
# Your code here

Need a hint?

Just create a variable with the exact name and value.

3

CORE LOGIC: Create POST route to add tasks with length check

Write a POST route /add-task that accepts a JSON body with a task string. Add the task to the tasks list only if its length is greater than or equal to MIN_TASK_LENGTH. Return {'success': True} if added, else {'success': False, 'error': 'Task too short'}.

FastAPI

from fastapi import FastAPI
from fastapi import Request

app = FastAPI()

tasks = ['buy milk', 'read book', 'write code']

MIN_TASK_LENGTH = 5

# Create POST route /add-task
# Your code here

Need a hint?

Use @app.post decorator and async function with request.json() to get the task.

4

COMPLETION: Write a test to verify task addition logic

Import TestClient from fastapi.testclient. Create a test function called test_add_task() that uses TestClient(app) to post a short task 'eat' and check the response JSON has 'success': False. Then post a valid task 'exercise' and check the response JSON has 'success': True.

FastAPI

from fastapi import FastAPI
from fastapi import Request
from fastapi.testclient import TestClient

app = FastAPI()

tasks = ['buy milk', 'read book', 'write code']

MIN_TASK_LENGTH = 5

@app.post('/add-task')
async def add_task(request: Request):
    data = await request.json()
    task = data.get('task', '')
    if len(task) >= MIN_TASK_LENGTH:
        tasks.append(task)
        return {'success': True}
    else:
        return {'success': False, 'error': 'Task too short'}

# Write test function test_add_task
# Your code here

Need a hint?

Use TestClient to simulate POST requests and assert to check responses.