Harden Your FastAPI

Add automated tests, middleware, atomic file writes, CORS, environment config, and global error handling to your expense tracker API.

Intermediate

3.5 hours

3 lessons

Course Content

22 chapters across 3 lessons

Test Your API

Write automated tests for your expense tracker using pytest and FastAPI's TestClient

10 chapters

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Why Test an API?

Continue

Understand why manual testing breaks down and how automated tests solve it

Install pytest

Install pytest and httpx in your terminal

Test Your Validator

Write unit tests that verify your custom date validator works correctly

Your First Endpoint Test

Use TestClient to send a POST request and verify the response

Test List and Filter

Write tests for listing expenses and filtering by category

Test Get Expense

Write a test for retrieving a single expense by its identifier

Test Delete Expense

Write a test for deleting an expense and verifying it is gone

Test Update

Write a test for the PATCH endpoint that partially updates an expense

Test Error Cases

Write tests that verify your API returns the correct errors for invalid requests

Lesson Complete

You finished Test Your API

Middleware & Reliability

Add request logging, atomic file writes, and CORS headers to your API

6 chapters

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What Is Middleware?

Understand how middleware wraps every request and response in your API

Request Logging Middleware

Add middleware that logs every request with its method, path, status, and duration

Test the Logging Middleware

Write a test that verifies the middleware does not break your API responses

Atomic File Writes

Rewrite save_expenses to use atomic file operations that prevent data corruption

CORS Headers

Add CORS middleware so browsers can call your API from a different domain

Lesson Complete

You finished Middleware & Reliability

Configuration & Error Handling

Move settings to environment variables and add a global exception handler

6 chapters

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Hardcoded Settings Are a Problem

Understand why hardcoded values like file paths and app titles should live in configuration

Create the Settings Class

Define a Settings class that reads configuration from environment variables

Use Settings in Your App

Replace hardcoded values with settings from your configuration class

Global Exception Handler

Add a catch-all handler that returns consistent JSON for any unhandled error

Test the Error Handler

Write a test that triggers an unhandled error and verifies the consistent response

Lesson Complete

You finished Configuration & Error Handling