REST Assured is a popular Java library used for API Automation Testing. It provides an easy way to test RESTful web services and validate responses using a simple and readable syntax.

1. What is REST Assured?

REST Assured is an open-source Java library specifically designed for testing REST APIs. It helps automate API validation without writing complex HTTP client code.

Key Features

• Easy API request creation
• JSON and XML validation support
• BDD-style syntax
• Integration with TestNG and JUnit
• Authentication support
• Schema validation

Example

given()
.when()
    .get("https://api.example.com/users")
.then()
    .statusCode(200);

2. API Testing Fundamentals

API Testing ensures that APIs work correctly, return expected data, handle errors properly, and meet performance requirements.

Benefits of API Testing

• Faster than UI testing
• Early defect detection
• Better backend validation
• Improved software quality
• Reduced testing costs

What Should Be Validated?

• Status Codes
• Response Body
• Response Headers
• Response Time
• Authentication
• Error Handling

3. HTTP Methods

GET

Used to retrieve data from the server.

given()
.when()
    .get("/users")
.then()
    .statusCode(200);

POST

Used to create a new resource.

String payload = "{ \"name\": \"John\" }";

given()
    .body(payload)
.when()
    .post("/users")
.then()
    .statusCode(201);

PUT

Used to completely update an existing resource.

given()
    .body(updatedPayload)
.when()
    .put("/users/1")
.then()
    .statusCode(200);

PATCH

Used to partially update a resource.

given()
    .body(partialPayload)
.when()
    .patch("/users/1")
.then()
    .statusCode(200);

DELETE

Used to remove a resource.

given()
.when()
    .delete("/users/1")
.then()
    .statusCode(204);

4. Request-Response Lifecycle

The API communication process follows these steps:

1. Client sends HTTP Request
2. Server receives the request
3. Business logic executes
4. Database interaction occurs
5. Server generates response
6. Client validates response

Client
   |
HTTP Request
   |
Server
   |
Business Logic
   |
Database
   |
HTTP Response
   |
Client

5. Maven Setup

Maven is a build automation and dependency management tool for Java projects.

Steps to Create a Maven Project

1. Open IntelliJ IDEA or Eclipse
2. Create a New Maven Project
3. Provide GroupId and ArtifactId
4. Generate Project Structure

Project Structure

project-name
│
├── src
│   ├── main
│   └── test
│
├── pom.xml
└── target

6. Adding REST Assured Dependencies

Add the following dependencies in the pom.xml file:

<dependency>
    <groupId>io.rest-assured</groupId>
    <artifactId>rest-assured</artifactId>
    <version>5.5.0</version>
    <scope>test</scope>
</dependency>

<dependency>
    <groupId>org.testng</groupId>
    <artifactId>testng</artifactId>
    <version>7.10.2</version>
    <scope>test</scope>
</dependency>

Verification Test

import static io.restassured.RestAssured.*;

@Test
public void verifyAPI() {

    given()
    .when()
        .get("https://reqres.in/api/users/2")
    .then()
        .statusCode(200);
}

Conclusion

REST Assured simplifies API automation testing in Java. Understanding API fundamentals, HTTP methods, request-response lifecycle, Maven setup, and dependency management creates a strong foundation for advanced REST Assured topics.