Getting Started with API Testing using Postman

What is an API?

An API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate with each other. In web development, we most often work with web APIs (like REST or GraphQL) that allow a client (like a web browser or mobile app) to request data from and send data to a server.

Why Test APIs?

Testing the API directly, without going through the UI, offers several advantages:

• Faster: API tests are significantly faster to run than end-to-end UI tests.
• More Stable: They are less brittle because they aren't affected by UI changes.
• Earlier Feedback: You can test business logic and data handling before a single pixel is drawn on the screen.

Introducing Postman

Postman is a powerful tool that simplifies the process of working with APIs. It provides a user-friendly interface to send requests, view responses, and organize your testing efforts.

Core Features:

• Request Builder: Easily construct requests of any type (GET, POST, PUT, DELETE, etc.), add headers, query parameters, and body data.
• Collections: Group your API requests together into collections to organize your workspace. You can run an entire collection at once.
• Environments: Manage variables like base URLs, API keys, and authentication tokens across different environments (e.g., local, staging, production).
• Tests and Scripts: Write JavaScript code to run after a request is completed. This is where the real testing power lies. You can write assertions to verify the status code, response body, headers, and more.

A Simple Test in Postman

In the "Tests" tab of a request, you can write JavaScript assertions.

// Check for a 200 OK status code
pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

// Check that the response body contains a specific property
pm.test("Response has user ID", function () {
    var jsonData = pm.response.json();
    pm.expect(jsonData).to.have.property('userId');
});

Postman is an essential tool for any developer or QA engineer working with APIs. It streamlines the entire lifecycle of API development, from design and mocking to testing and documentation.