Practical Guide to API Testing

API testing ensures backend services function correctly and reliably. This guide covers everything you need — from HTTP codes to Postman automation and Rest Assured scripting.

🔹 Common HTTP Status Codes & Meanings

1. ✅ 200 OK – Request successful
2. 🔄 201 Created – New resource created
3. ⚠ 400 Bad Request – Invalid request syntax
4. 🚫 401 Unauthorized – Authentication required
5. ❌ 404 Not Found – Resource does not exist
6. 💥 500 Internal Server Error – Unexpected server issue

🔗 Live APIs for Testing

1. JSONPlaceholder – Fake API for testing
2. ReqRes – User management testing
3. HTTP Stat.us – Simulate HTTP status codes

🛠 Using Postman for API Testing

1. Install Postman & create a new request
2. Select method (GET, POST, etc.) & enter API URL
3. Add parameters or body if needed
4. Click Send & check response
5. Write assertions in the Tests tab:

// Example Postman Test

pm.test("Status code is 200", function () {

pm.response.to.have.status(200);

});

Use Postman Collection Runner to automate and run tests in batches.

🤖 Using Rest Assured for API Automation (Java)

📌 Maven Dependency:

io.rest-assured

rest-assured

4.4.0

test

📌 Basic Test Example:

import static io.restassured.RestAssured.*;

import static org.hamcrest.Matchers.*;

public class ApiTest {

public static void main(String[] args) {

given()

.when()

.get("https://jsonplaceholder.typicode.com/posts/1")

.then()

.statusCode(200)

.body("userId", equalTo(1));

}

}

🏆 Key API Testing Concepts

1. ✔ Validate Response Codes & Body
2. ✔ Header Validation & Authentication
3. ✔ Negative Testing for invalid inputs
4. ✔ Data-Driven Testing with CSV/JSON

📊 Advanced API Testing Techniques

1. 🔹 Mock APIs using Postman Mock Servers
2. 🔹 Integrate Postman with CI/CD using Newman
3. 🔹 Generate Reports using Extent Reports in Rest Assured

🚀 API testing plays a vital role in ensuring application reliability. Whether using Postman for manual testing or Rest Assured for automation, mastering these tools boosts quality and efficiency.

❓ Frequently Asked Questions (FAQs)

1️⃣ What is API Testing?

It’s the process of verifying APIs for correctness, reliability, and performance — ensuring communication between services works as expected.

2️⃣ What tools are used for API Testing?

Popular tools include Postman, Rest Assured, SoapUI, and Newman for CI/CD automation.

3️⃣ What are common HTTP request methods?

GET (read), POST (create), PUT (update), DELETE (remove), and PATCH (partial update).

4️⃣ Can API Testing be automated?

Yes. Rest Assured, Postman + Newman, and other frameworks enable complete automation integrated into CI/CD pipelines.