11.1. What is an API?

An API (Application Programming Interface) allows different software systems to communicate with each other. In QA, we primarily test REST APIs which follow the HTTP protocol and return data in JSON or XML format.

An API acts like a bridge between different software applications, allowing them to talk to each other and exchange data. In the context of Quality Assurance (QA), we focus on testing REST APIs. REST stands for Representational State Transfer, which utilizes standard HTTP protocols for communication and typically returns data in formats like JSON or XML, making it easier for systems to understand and process the information.

Think of an API like a restaurant menu. The menu provides a list of dishes (functions) you can order (request). When you place an order (send a request), the kitchen (the back-end system) prepares the food (processes the request) and serves it to you (returns a response). Just like you expect a particular dish to be prepared in a certain way, systems rely on APIs to provide the correct data in a specified format.

🔹 REST (Representational State Transfer) is: ● Stateless: Each call is independent ● Resource-Based: Uses URLs to identify resources ● Uses HTTP methods: GET, POST, PUT, DELETE

REST APIs have three key characteristics: they are stateless, resource-based, and utilize standard HTTP methods. Being stateless means that each API call is treated independently, with no previous context needed. The resource-based nature means resources (such as data entities) are identified using URLs. Finally, REST APIs rely on standard HTTP methods. Each method serves a specific purpose, such as retrieving data (GET), sending new data (POST), updating existing data (PUT), or deleting data (DELETE).

Imagine using a library where each book is a unique resource. Each time you want to borrow a book (resource), you simply go to its shelf using a specific location (URL). You don’t need to remember previous transactions (stateless). When you check out a book (GET), return it (DELETE), or request a new one (POST), you use a straightforward process that everyone knows (HTTP methods).

M Purpose Example et ho D G Retrieve data Get all users E E T P Submit/create Create a new O new data account S T P Update existing Update user U data profile T D Remove data Delete a user E record

In APIs, different HTTP methods define the type of operation being performed. The most common methods include GET (to retrieve data), POST (to create new data), PUT (to update existing data), and DELETE (to remove data). For instance, if you want to get a list of all users, you would use the GET method. When creating a new user account, you'd send a POST request with the user's details. If you need to modify an existing user profile, you would use PUT, and to remove a user, the DELETE method is appropriate.

Consider an online shopping website. When you want to view items, you click 'Browse' (GET). When you add an item to your cart, you’re creating a request (POST). If you decide to change the quantity, you update your cart (PUT). Finally, when you remove an item you no longer want, you’re deleting it from your cart (DELETE). Each action corresponds to an HTTP method.

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