Practical Guide to API Testing

API testing ensures backend services function correctly and reliably. Here's a step-by-step guide to mastering API testing using Postman and Rest Assured!

🔹 Common HTTP Status Codes & Meanings

• ✅ 200 OK – Request successful
• 🔄 201 Created – New resource created
• ⚠ 400 Bad Request – Invalid request syntax
• 🚫 401 Unauthorized – Authentication required
• ❌ 404 Not Found – Resource does not exist
• 💥 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 the API URL.
3. Add parameters or a request body if needed.
4. Click "Send" and examine the response.
5. Write assertions in the "Tests" tab:

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

6. Automate testing using Postman's Collection Runner.

🤖 Using Rest Assured for API Automation (Java)

📌 Maven Dependency (Add this to pom.xml):

<dependency>
    <groupId>io.rest-assured</groupId>
    <artifactId>rest-assured</artifactId>
    <version>4.4.0</version>
    <scope>test</scope>
</dependency>

📌 Basic Test Case:

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

• Validate Response Codes & Body
• Header Validation & Authentication
• Negative Testing – Ensure the API handles invalid requests properly
• Data-Driven Testing – Use CSV/JSON inputs for test cases

📊 Advanced API Testing Techniques

• Mock APIs using Postman Mock Servers
• CI/CD Integration using Newman (Postman CLI)
• Automated Reporting with Extent Reports for Rest Assured

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🚀 API testing is critical for software reliability. Whether using Postman for manual testing or Rest Assured for automation, mastering these skills helps deliver high-quality applications.