Applying API Testing Frameworks: Real-World Examples Using Postman

In the API-driven world of modern software, backend services are only as reliable as the tests we write for them. Whether you’re building a microservice or a full RESTful API, API testing is essential to validate your endpoints, responses, and business logic.

In this article, I’ll walk you through how to use Postman—one of the most popular API testing frameworks—to create real-world API tests with practical examples and code.

🔹Why Use a Framework Like Postman?

Postman allows developers and QA engineers to:

Create and send HTTP requests to an API
Write automated test scripts in JavaScript
Organize requests into collections
Use environments and variables to test across stages (dev, staging, production)

It combines ease of use with powerful features for testing REST, GraphQL, and SOAP APIs.

🔹Real-World API Testing Scenario

Let’s assume you’re building an API for a bookstore. You have this endpoint:

GET https://api.mybookstore.com/books

Your goal is to verify that:

The server responds with HTTP 200
The response body is JSON
Each book object has a title, author, and price

🔹Creating a Test in Postman

After sending the request in Postman, go to the Tests tab and write:

pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

pm.test("Response is JSON", function () {
    pm.response.to.be.json;
});

pm.test("Each book has required fields", function () {
    const books = pm.response.json();
    books.forEach(book => {
        pm.expect(book).to.have.property("title");
        pm.expect(book).to.have.property("author");
        pm.expect(book).to.have.property("price");
    });
});

These scripts use Postman’s built-in Chai.js assertion library to check the API response.

🔹Testing with Parameters and Edge Cases

Let’s test a filtered request like:

GET https://api.mybookstore.com/books?author=Orwell
You can write a test to ensure that all returned books are from that author:

pm.test("Books returned are by Orwell", function () {
    const books = pm.response.json();
    books.forEach(book => {
        pm.expect(book.author).to.eql("Orwell");
    });
});

This is a real-world example of validating query parameters and filtering logic in the backend.

🔹Using Environments for Flexibility

You can define variables in Postman environments like:

base_url = https://api.mybookstore.com

Then, in your requests:

{{base_url}}/books

This allows you to reuse the same tests for: