How to Test a POST API by Rest Assured

What is a POST API?

A POST API is an HTTP endpoint that allows a client to send data to the server.
The data is usually sent in the request body in formats like JSON, XML, or form data.
Common uses of POST APIs:

Creating a new resource (e.g., creating a new user in a system).

Submitting forms (login, registration, etc.).

Sending files or data for processing.

How to Test a POST API in Rest Assured

When testing a POST API in Rest Assured, you typically perform these steps:

1. Set the Base URI

Define the API host (e.g., https://reqres.in).

2. Define the Request Body

Prepare the JSON (or other format) data that you want to send.

3. Send the POST Request

Use Rest Assured to send the request to the endpoint (e.g., /api/users).

4. Validate Response Status Code

Check if the response code is correct (usually 201 Created for a successful POST).

5. Verify Response Body

Ensure the response contains the expected data (like the new id or confirmation message).

6. Check Response Headers (Optional)

Validate Content-Type, Location, etc., to ensure proper response formatting.

To test a POST API using Rest Assured with a JSONObject in Java, follow these steps:

Step-by-Step Implementation

1. Add Rest Assured Dependency

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

    <!-- JSON Library -->
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20230618</version>
    </dependency>
</dependencies>

API to be tested:

POST https://reqres.in/api/users

Sample request body:

{
  "name": "Himanshu",
  "job": "QA Engineer"
}

Expected response (201 Created):

{
  "name": "Himanshu",
  "job": "QA Engineer",
  "id": "123",
  "createdAt": "2025-07-28T..."
}

3. Java Code to Test POST API using JSONObject

import io.restassured.RestAssured;
import io.restassured.response.Response;
import io.restassured.http.ContentType;
import org.json.JSONObject;

public class PostAPITest {

    public static void main(String[] args) {

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

        // Step 2: Create Request Payload using JSONObject
        JSONObject requestBody = new JSONObject();
        requestBody.put("name", "Himanshu");
        requestBody.put("job", "QA Engineer");

        // Step 3: Make POST Request
        Response response = RestAssured
            .given()
                .contentType(ContentType.JSON)
                .body(requestBody.toString())
                .log().all()
            .when()
                .post("/users")
            .then()
                .log().all()
                .statusCode(201)
                .extract().response();

        // Step 4: Print Response Fields
        System.out.println("ID: " + response.jsonPath().getString("id"));
        System.out.println("Created At: " + response.jsonPath().getString("createdAt"));
    }
}

Code Explanation:

Line	Purpose
RestAssured.baseURI	Sets the base URL.
JSONObject	Builds the JSON body using key-value pairs.
given().contentType().body()	Prepares the request with headers and body.
post("/users")	Sends POST request to the endpoint.
statusCode(201)	Verifies the response status.
response.jsonPath()	Extracts values from JSON response.

Sample Output:

Request method:	POST
Request URI:	https://reqres.in/api/users
Request body:
{
    "name": "Himanshu",
    "job": "QA Engineer"
}
Response Status Code: 201
Response body:
{
    "name": "Himanshu",
    "job": "QA Engineer",
    "id": "867",
    "createdAt": "2025-07-28T14:30:55.098Z"
}