One of the most popular tools for automated API testing in Java is Rest Assured — a powerful and easy-to-use library that allows you to write API tests directly in code. It supports HTTP methods, request validation, and detailed assertions in a clean, readable syntax.
In this article, we’ll walk through how to set up and run API tests using Rest Assured with simple examples based on the PetStore API, a well-known demo application for practicing CRUD operations.
⚙️ Prerequisites
Run the Petstore API Demo Locally
First, let’s start by running a Petstore API Demo that we can test.
If you haven’t already, clone and run the Petstore API Demo
Once the application is running, you can open:
- Swagger UI: http://localhost:8080/api/v1/swagger-ui/index.html#/
- API documentation (OpenAPI JSON): http://localhost:8080/api/v1/api-docs
make sure you have:
- Java 17+ installed
- Maven or (Gradle) for project setup
- A code editor like IntelliJ IDEA or VS Code with Java extensions
- Basic understanding of REST APIs
✅ 1. Set Up Your Maven Project
<dependencies>
<dependency>
<groupId>io.rest-assured</groupId>
<artifactId>rest-assured</artifactId>
<version>5.4.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.testng</groupId>
<artifactId>testng</artifactId>
<version>7.10.2</version>
<scope>test</scope>
</dependency>
</dependencies>
This will include Rest Assured for API testing and TestNG for test organization and execution.
✅ 2. Write Your API Tests
Let’s write a few API test scenarios for the PetStore API, similar to what we did in Postman.
We’ll cover:
- Add a new pet to the store
- Update an existing pet
- Find pet by ID
- Delete Pet
- Pet not found
package com.petstore.rest_assured.api_tests;
import io.restassured.RestAssured;
import io.restassured.response.Response;
import org.testng.annotations.BeforeClass;
import org.testng.annotations.Test;
import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;
public class PetStoreApiTests {
private static Long petId;
@BeforeClass
public void setup() {
RestAssured.baseURI = "http://localhost:8080/api/v1";
}
// Add a new pet
@Test(priority = 1)
public void testAddNewPet() {
String requestBody = """
{
"id": 4677,
"name": "fluffy",
"status": "New",
"photoUrls": [
"Photo1",
"Photo1"
],
"category": {
"id": 9342,
"name": "ABC"
},
"tags": [
{
"name": "PET",
"id": 2875
},
{
"name": "STORE",
"id": 7063
}
]
}
""";
Response response = given()
.contentType("application/json")
.body(requestBody)
.when()
.post("/pet")
.then()
.statusCode(200)
.body("name", equalTo("fluffy"))
.extract().response();
petId = response.jsonPath().getLong("id");
System.out.println("Created Pet ID: " + petId);
}
// Update an existing pet
@Test(priority = 2, dependsOnMethods = "testAddNewPet")
public void testUpdatePet() {
String requestBody = String.format("""
{
"id": %d,
"name": "fluffy-updated",
"status": "SOLD",
"photoUrls": [
"Photo1",
"Photo1"
],
"category": {
"id": 9342,
"name": "ABC"
},
"tags": [
{
"name": "PET",
"id": 2875
},
{
"name": "STORE",
"id": 7063
}
]
}
""", petId);
given()
.contentType("application/json")
.body(requestBody)
.when()
.put("/pet")
.then()
.statusCode(200)
.body("name", equalTo("fluffy-updated"))
.body("status", equalTo("SOLD"));
}
// Find pet by ID
@Test(priority = 3, dependsOnMethods = "testUpdatePet")
public void testFindPetById() {
given()
.pathParam("petId", petId)
.when()
.get("/pet/{petId}")
.then()
.statusCode(200)
.body("id", equalTo(petId.intValue()));
}
// Delete Pet
@Test(priority = 4, dependsOnMethods = "testFindPetById")
public void testDeletePet() {
given()
.pathParam("petId", petId)
.when()
.delete("/pet/{petId}")
.then()
.statusCode(200);
}
// Pet not found
@Test(priority = 5)
public void testPetNotFound() {
given()
.pathParam("petId", petId)
.when()
.get("/pet/{petId}")
.then()
.statusCode(404)
.body("message", equalTo("Pet not found with id: " + petId));
}
}
✅ 3. Run the Test
To execute your tests, open a terminal in your project directory and run: below command or run it off form your IDE
mvn test🧭 Conclusion
Rest Assured is a powerful tool for automating API testing directly within your codebase.
Unlike Postman collections, it allows you to:
- Write tests programmatically
- Reuse code and data structures
- Integrate easily into CI/CD pipelines
If you’re comfortable with Java, this is one of the most scalable ways to build automated API test suites.