API Testing Techniques Tutorial

1. Introduction

• This tutorial aims to provide you with in-depth knowledge on API Testing Techniques. We will cover the basics and walk through various techniques of API testing that you can employ to ensure that your web applications are functioning as intended.

• After this tutorial, you will be able to understand what API testing is, why it is important, and how to effectively carry out API tests using different techniques.

• Prerequisites: Basic understanding of APIs, HTTP methods, and some familiarity with a programming language (preferably Python or JavaScript).

2. Step-by-Step Guide

API (Application Programming Interface) Testing is a software testing type which focuses on the determination if the developed APIs meet expectations regarding functionality, reliability, performance, and security of the application.

Concept Overview

1. Validation Testing: This ensures that the API's functionality is working as expected and the inputs correspond to the proper output.
2. UI Testing: Ensures the user interface of the API functions properly.
3. Security Testing: Checks any potential threats and vulnerabilities in the API.
4. Load Testing: Verifies the performance of the API under load.

Best Practices and Tips

• Always validate your API against a schema.
• Automate your API tests as much as possible.
• Regularly update your test cases as the API evolves.

3. Code Examples

Here, we will use Python and the requests library for our API testing examples.

Example 1: Testing a GET request

import requests
# Sending a GET request
response = requests.get('http://api.example.com/users')

# Check the status code
assert response.status_code == 200, 'Status code is not 200'

# Check the returned data
assert 'John Doe' in response.text, 'John Doe is not in the response'

This code sends a GET request to the /users endpoint of our API and checks if the status code is 200 and if 'John Doe' is in the response.

Example 2: Testing a POST request

import requests
import json
# Define the data to send
data = {'name': 'John Doe', 'email': 'john@example.com'}

# Send a POST request
response = requests.post('http://api.example.com/users', data=json.dumps(data))

# Check the status code
assert response.status_code == 201, 'Status code is not 201'

# Check the returned data
assert 'John Doe' in response.text, 'John Doe is not in the response'

This code sends a POST request to the /users endpoint of our API, creating a new user. It checks if the status code is 201 (indicating successful creation) and if 'John Doe' is in the response.

4. Summary

You've learned what API testing is, why it's essential, and how to perform API testing using Python and requests. You also learned about different API testing techniques like validation, UI, security, and load testing.

5. Practice Exercises

To solidify what you've learned, try these exercises:

1. Write a test case for an API that deletes a user. Check if the status code is 204 and the user is no longer in the database.
2. Write a test case for an API that updates user information. Check if the status code is 200 and the user information has been updated in the response.

Remember to check the documentation of the API you're testing to understand what results to expect and what data to send.

Happy testing!