Beginner Chapter 6 · 9 min read

Headers & Content Types

Set and validate request/response headers, work with different content types (JSON, XML, form data), and understand common HTTP headers.

HTTP Headers in API Testing

HTTP headers carry metadata about the request and response. They control content negotiation, authentication, caching, and more. Understanding headers is essential for proper API testing.

Common Request Headers

Content-Type — Format of the request body (application/json, multipart/form-data, application/x-www-form-urlencoded)
Accept — What response formats the client can handle
Authorization — Authentication credentials (Bearer token, Basic auth)
User-Agent — Client identification
X-Custom-Header — Application-specific custom headers

Common Response Headers

Content-Type — Format of the response body
Content-Length — Size of the response in bytes
Cache-Control — Caching directives
X-RateLimit-* — Rate limiting information
Set-Cookie — Session cookies

headers.test.js

// Setting request headers
const response = await fetch('https://jsonplaceholder.typicode.com/posts', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Accept': 'application/json',
    'X-Custom-Header': 'test-value',
    'User-Agent': 'API-Test-Suite/1.0'
  },
  body: JSON.stringify({ title: 'Test', body: 'Content', userId: 1 })
});

// Validate response headers
console.assert(
  response.headers.get('content-type').includes('application/json'),
  'Response should be JSON'
);
console.log('Content-Type:', response.headers.get('content-type'));

// Iterate through all response headers
for (const [key, value] of response.headers.entries()) {
  console.log(`  ${key}: ${value}`);
}

// Form URL-encoded data
const formData = new URLSearchParams();
formData.append('username', 'testuser');
formData.append('password', 'testpass');

const formResponse = await fetch('https://httpbin.org/post', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded'
  },
  body: formData.toString()
});

const formResult = await formResponse.json();
console.log('Form data received:', formResult.form);

HeadersTest.java

import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;
import io.restassured.http.ContentType;
import io.restassured.response.Response;
import org.testng.annotations.Test;

public class HeadersTest {

    @Test
    public void testRequestHeaders() {
        given()
            .baseUri("https://jsonplaceholder.typicode.com")
            .contentType(ContentType.JSON)
            .accept(ContentType.JSON)
            .header("X-Custom-Header", "test-value")
            .header("User-Agent", "API-Test-Suite/1.0")
            .body("{ \"title\": \"Test\", \"body\": \"Content\", \"userId\": 1 }")
        .when()
            .post("/posts")
        .then()
            .statusCode(201)
            .contentType(ContentType.JSON);
    }

    @Test
    public void testResponseHeaders() {
        Response response =
            given()
                .baseUri("https://jsonplaceholder.typicode.com")
            .when()
                .get("/posts/1")
            .then()
                .header("Content-Type", containsString("application/json"))
                .extract().response();

        // Access individual headers
        String contentType = response.getHeader("Content-Type");
        System.out.println("Content-Type: " + contentType);

        // Get all headers
        response.getHeaders().forEach(h ->
            System.out.println("  " + h.getName() + ": " + h.getValue())
        );
    }

    @Test
    public void testFormUrlEncoded() {
        given()
            .baseUri("https://httpbin.org")
            .contentType("application/x-www-form-urlencoded")
            .formParam("username", "testuser")
            .formParam("password", "testpass")
        .when()
            .post("/post")
        .then()
            .statusCode(200)
            .body("form.username", equalTo("testuser"));
    }
}

test_headers.py

import requests

def test_request_headers():
    """Setting custom request headers"""
    headers = {
        'Content-Type': 'application/json',
        'Accept': 'application/json',
        'X-Custom-Header': 'test-value',
        'User-Agent': 'API-Test-Suite/1.0'
    }

    response = requests.post(
        'https://jsonplaceholder.typicode.com/posts',
        headers=headers,
        json={'title': 'Test', 'body': 'Content', 'userId': 1}
    )

    assert response.status_code == 201
    assert 'application/json' in response.headers['Content-Type']

def test_response_headers():
    """Validate response headers"""
    response = requests.get('https://jsonplaceholder.typicode.com/posts/1')

    # Access individual headers (case-insensitive)
    print(f"Content-Type: {response.headers['Content-Type']}")

    # Iterate all response headers
    for key, value in response.headers.items():
        print(f"  {key}: {value}")

    assert 'application/json' in response.headers['Content-Type']

def test_form_urlencoded():
    """Submit form-urlencoded data"""
    response = requests.post(
        'https://httpbin.org/post',
        data={'username': 'testuser', 'password': 'testpass'}
    )

    assert response.status_code == 200
    assert response.json()['form']['username'] == 'testuser'

API Testing Beginner Headers & Content Types

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Written by PV