How to Test GET API by Rest Assured

What is Rest Assured?

Rest Assured is a Java-based library used for testing RESTful APIs.
It provides a domain-specific language (DSL) that makes writing HTTP request tests simple and readable.
You can use it to send requests like GET, POST, PUT, DELETE, etc., and then validate responses (status code, headers, body, etc.).
It integrates well with JUnit, TestNG, Maven, and CI/CD tools.

To test a GET API using Rest Assured in Java, you can follow the steps below. We'll walk through the process and test the endpoint:

API Endpoint: https://reqres.in/api/users

This API returns paginated user data in JSON format.

Basic Steps to Test GET API

Add Rest Assured dependency in your pom.xml (if using Maven).
Set the Base URI.
Send the GET request.
Validate the Response (status code, headers, body).
Log response (optional but useful for debugging).

Maven Dependency (pom.xml):

<dependencies>
    <dependency>
        <groupId>io.rest-assured</groupId>
        <artifactId>rest-assured</artifactId>
        <version>5.3.0</version>
        <scope>test</scope>
    </dependency>
</dependencies>

Java Code to Test GET API

import io.restassured.RestAssured;
import io.restassured.response.Response;

import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;

public class GetUserApiTest {

    public static void main(String[] args) {

        // Step 1: Set Base URI
        RestAssured.baseURI = "https://reqres.in";

        // Step 2: Send GET request and validate
        given()
            .log().all()  // Logs the request details
        .when()
            .get("/api/users?page=2")  // Endpoint
        .then()
            .log().all()  // Logs the response details
            .assertThat()
            .statusCode(200)  // Validate HTTP Status code
            .body("data", notNullValue())  // Validate response body contains 'data'
            .body("data.size()", greaterThan(0))  // Validate non-empty data
            .body("data[0].id", notNullValue());  // Validate user id present
    }
}

Explanation of Code:

Line	Purpose
baseURI	Sets the base URL for the request.
given()	Prepares request specification.
log().all()	Logs all request and response data for visibility.
get()	Triggers the GET request to the specified endpoint.
then()	Begins response verification.
statusCode(200)	Verifies the status code is 200 (OK).
body(...)	Verifies the presence and contents of specific JSON fields.

Response Validation:

Below is the screenshot of code which is validating GET API response.

In above screenshot, data is json array, and code is validating that data contains any values or not or we can say it is null or not. In the second line we are verifying size of array data is greater than 0 or not and in third line we are verifying, first element of data array that is id, is null or contains any value.

Sample JSON Output from API

{
  "page": 2,
  "per_page": 6,
  "data": [
    {
      "id": 7,
      "email": "michael.lawson@reqres.in",
      "first_name": "Michael",
      "last_name": "Lawson",
      ...
    }
  ]
}