How to Use WireMock with JUnit Test?

WireMock is a tool for mocking HTTP-based APIs that runs in the unit tests, on the desktop, or in the test environment. We can also say it is a simulator for HTTP-based APIs, considered a service virtualization tool or a mock server. It enables you to stay productive when an API you depend on Doesn't exist and, Isn't complete or, Costly to access. It supports the testing of Edge cases and failure modes. It's fast so reduces build time significantly. In simple terms, Wiremock is a mocking setup for integration testing. It is mainly used during the development and more significantly during the Integration testing while a system or service talks to one or multiple external or internal dependencies/services.

Read more about WireMock in this article: Introduction to WireMock

In this article, we are going to use WireMock with JUnit Test. JUnit framework is a Java framework that is widely used for testing. It supports the test to run by writing and testing along. JUnit framework was initially based on the SUnit framework which is used for Unit testing but then later it was updated with Java using Selenium WebDriver. JUnit is now used as a standard when we need to perform testing in Java.

Step By Step Implementation 

Step 1: Refer to the article How to Create a Maven Project in IntelliJ IDEA and create a Maven project in IntelliJ IDEA. 

Step 2: Add the following dependencies in your pom.xml file.

<!-- Dependency for okhttp -->
<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.2.2</version>
</dependency>

<!-- Dependency for Wiremock-->
<dependency>
    <groupId>com.github.tomakehurst</groupId>
    <artifactId>wiremock</artifactId>
    <version>2.27.2</version>
    <scope>test</scope>
</dependency>

<!-- Dependency for JUnit-->
<dependency>
   <groupId>junit</groupId>
   <artifactId>junit</artifactId>
   <version>4.13-rc-2</version>
   <scope>test</scope>
</dependency>

Below is the complete code for the pom.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                             http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>wiremock-with-junit</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>

    <dependencies>

        <dependency>
            <groupId>com.squareup.okhttp3</groupId>
            <artifactId>okhttp</artifactId>
            <version>4.2.2</version>
        </dependency>

        <dependency>
            <groupId>com.github.tomakehurst</groupId>
            <artifactId>wiremock</artifactId>
            <version>2.27.2</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13-rc-2</version>
            <scope>test</scope>
        </dependency>      

    </dependencies>

</project>

Step 3: Now go to the src > test > java and create a test class named WiremockWithJunit. In this class, we are going to perform the JUnit test using WireMock. First, refer to the whole code then we will understand the code in detail.

import com.github.tomakehurst.wiremock.junit.WireMockRule;
import okhttp3.*;
import org.junit.Rule;
import org.junit.Test;

import static com.github.tomakehurst.wiremock.client.WireMock.*;
import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.wireMockConfig;
import static org.junit.Assert.assertEquals;

public class WiremockWithJunit {

    @Rule
    public WireMockRule wireMockRule = new WireMockRule(wireMockConfig().port(9090));

    // WireMock with JUnit
    @Test
    public void wiremock_with_junit_test() throws Exception {
        // stub configuration
        configStub();

        // call request in WireMock through OkHttpClient
        OkHttpClient client = new OkHttpClient().newBuilder()
                .build();
        Request request = new Request.Builder()
                .url("http://localhost:9090/gfg/article1")
                .method("GET", null)
                .build();

        Response response = client.newCall(request).execute();

        // assert the response
        assertEquals("Welcome to GeeksforGeeks!!", response.body().string());
    }

    private void configStub() {
        configureFor("localhost", 9090);
        // create a stub
        stubFor(get(urlEqualTo("/gfg/article1")).willReturn(aResponse().withBody("Welcome to GeeksforGeeks!!")));
    }
 
}

Explanation: A Rule is nothing but a concept in JUnit which actually combines test setup methods like @Before and @After. And WireMock by default provides a Rule for JUnit named WireMockRule. 

@Rule
public WireMockRule wireMockRule = new WireMockRule(wireMockConfig().port(9090));

Then we define a method wiremock_with_junit_test() and annotated it with @Test annotation. Because this is the method we are going to test. And inside this method, we are going to perform the following 3 task

• Arrange
• Act
• Assert

Arrange: At first, we configure the stub in configStub() method. Refer to the below code snippet. 

private void configStub() {
        configureFor("localhost", 9090);
        // create a stub
        stubFor(get(urlEqualTo("/gfg/article1")).willReturn(aResponse().withBody("Welcome to GeeksforGeeks!!")));
    }

Act: Then we call the request in WireMock through OkHttpClient. Refer to the below code snippet. 

OkHttpClient client = new OkHttpClient().newBuilder().build();
Request request = new Request.Builder()
                .url("http://localhost:9090/gfg/article1")
                .method("GET", null)
                .build();
Response response = client.newCall(request).execute();

Assert: Here we will assert the response. Refer to the below code snippet. 

assertEquals("Welcome to GeeksforGeeks!!", response.body().string());

Now, let's test the method. 

Output: Success Case

And you can see Test Passed in this case. Let's have a scenario with a Failure case.

Output: Failure Case

Now let's change the expected value to something like this. You can also change the actual value. 

assertEquals("Welcome to Hello World!!", response.body().string());

And in the output, you can see Test failed with the reason.