IN28MINUTES

Mockito Tutorial for Beginner in 5 Steps

Nov 17, 2017
6 minute read

Image Image

Mockito is the most popular mocking framework in Java.

Free Courses - Learn in 10 Steps

Git Repository

  • https://github.com/in28minutes/getting-started-in-5-steps/tree/master/mockito-in-5-steps

Pre-requisites

  • Java & Eclipse - https://www.youtube.com/playlist?list=PLBBog2r6uMCSmMVTW_QmDLyASBvovyAO3
  • JUnit - https://courses.in28minutes.com/p/junit-tutorial-for-beginners

IDE Configuration

Easier Static Imports

  • Window > Preferences > Java > Editor > Content Assist > Favorites
    • org.junit.Assert
    • org.mockito.BDDMockito
    • org.mockito.Mockito
    • org.hamcrest.Matchers
    • org.hamcrest.CoreMatchers

Reference

  • Visit Mockito Official Documentation - http://site.mockito.org/mockito/docs/current/org/mockito/Mockito.html

Overview

  • Step 1 : Setting up an example using http://start.spring.io.
  • Step 2 : Using a Stubs - Disadvantages
  • Step 3 : Your first mock.
  • Step 4 : Using Mockito Annotations - @Mock, @InjectMocks, @RunWith(MockitoJUnitRunner.class)
  • Step 5 : Mocking List interface

Step 1 : Setting up an example using http://start.spring.io.

Creating a Spring Project with Spring Initializr is a cake walk.

Spring Initializr http://start.spring.io/ is great tool to bootstrap your Spring Boot projects.

Image

As shown in the image above, following steps have to be done

  • Launch Spring Initializr and choose the following
    • Choose com.in28minutes.mockito as Group
    • Choose mockito-demo as Artifact
    • Choose Dependency
      • Web
  • Click Generate Project.
  • Import the project into Eclipse.
  • If you want to understand all the files that are part of this project, you can go here.

Let’s also set up a simple business class with a dependency.

  • SomeBusinessImpl depends on DataService for the data
  • findTheGreatestFromAllData has some business logic to find the greatest
package com.in28minutes.mockito.mockitodemo;

public class SomeBusinessImpl {
	private DataService dataService;

	public SomeBusinessImpl(DataService dataService) {
		super();
		this.dataService = dataService;
	}

	int findTheGreatestFromAllData() {
		int[] data = dataService.retrieveAllData();
		int greatest = Integer.MIN_VALUE;

		for (int value : data) {
			if (value > greatest) {
				greatest = value;
			}
		}
		return greatest;
	}
}

package com.in28minutes.mockito.mockitodemo;

public interface DataService {
	int[] retrieveAllData();
}

Step 2 : Using a Stubs - Disadvantages

Let’s use a stub to write a unit test for SomeBusinessImpl.

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class SomeBusinessStubTest {
	@Test
	public void testFindTheGreatestFromAllData() {
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(new DataServiceStub());
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(24, result);

	}

}

class DataServiceStub implements DataService {
	@Override
	public int[] retrieveAllData() {
		return new int[] { 24, 6, 15 };
	}
}

Problems with Stub

  • How do I get DataServiceStub to return different data for different scenaris?
  • Everytime DataService interface is updated with new methods, the DataServiceStub implementations should be updated.

Step 3 : Your first mock.

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import org.junit.Test;

public class SomeBusinessMockTest {

	@Test
	public void testFindTheGreatestFromAllData() {
		DataService dataServiceMock = mock(DataService.class);
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 3 });
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(dataServiceMock);
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(24, result);
	}

	@Test
	public void testFindTheGreatestFromAllData_ForOneValue() {
		DataService dataServiceMock = mock(DataService.class);
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 15 });
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(dataServiceMock);
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(15, result);
	}

}

Notes

  • DataService dataServiceMock = mock(DataService.class) - We are using the mock method to create a mock.
  • when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 3 }) - stubbing the mock to return specific data

Step 4 : Using Mockito Annotations - @Mock, @InjectMocks, @RunWith(MockitoJUnitRunner.class)

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.when;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class SomeBusinessMockAnnotationsTest {

	@Mock
	DataService dataServiceMock;

	@InjectMocks
	SomeBusinessImpl businessImpl;

	@Test
	public void testFindTheGreatestFromAllData() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 3 });
		assertEquals(24, businessImpl.findTheGreatestFromAllData());
	}

	@Test
	public void testFindTheGreatestFromAllData_ForOneValue() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 15 });
		assertEquals(15, businessImpl.findTheGreatestFromAllData());
	}

	@Test
	public void testFindTheGreatestFromAllData_NoValues() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] {});
		assertEquals(Integer.MIN_VALUE, businessImpl.findTheGreatestFromAllData());
	}
}

Notes

  • @Mock DataService dataServiceMock; - Create a mock for DataService.
  • @InjectMocks SomeBusinessImpl businessImpl; - Inject the mocks as dependencies into businessImpl.
  • @RunWith(MockitoJUnitRunner.class) - The JUnit Runner which causes all the initialization magic with @Mock and @InjectMocks to happen before the tests are run.

Step 5 : Mocking List interface

Mocking a method. Mock returns the same value on multiple calls.

@Test
public void testSize() {
	List listMock = mock(List.class);
	when(listMock.size()).thenReturn(10);
	assertEquals(10, listMock.size());
	assertEquals(10, listMock.size());
}

Setting the mock to return 10 on first call and 20 on the second call.

@Test
public void testSize_multipleReturns() {
	List listMock = mock(List.class);
	when(listMock.size()).thenReturn(10).thenReturn(20);
	assertEquals(10, listMock.size());
	assertEquals(20, listMock.size());
	assertEquals(20, listMock.size());
}

Customizing the mock based on a specific parameter value.

@Test
public void testGet_SpecificParameter() {
	List listMock = mock(List.class);
	when(listMock.get(0)).thenReturn("SomeString");
	assertEquals("SomeString", listMock.get(0));
	assertEquals(null, listMock.get(1));
}

Using a generic argument - Mockito.anyInt()

@Test
public void testGet_GenericParameter() {
	List listMock = mock(List.class);
	when(listMock.get(Mockito.anyInt())).thenReturn("SomeString");
	assertEquals("SomeString", listMock.get(0));
	assertEquals("SomeString", listMock.get(1));
}

Unit Testing Courses

Image

Complete Code Example

/pom.xml

<?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>com.in28minutes.mockito</groupId>
	<artifactId>mockito-demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>mockito-demo</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.0.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
		<java.version>1.8</java.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

	<repositories>
		<repository>
			<id>spring-snapshots</id>
			<name>Spring Snapshots</name>
			<url>https://repo.spring.io/snapshot</url>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</repository>
		<repository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</repository>
	</repositories>

	<pluginRepositories>
		<pluginRepository>
			<id>spring-snapshots</id>
			<name>Spring Snapshots</name>
			<url>https://repo.spring.io/snapshot</url>
			<snapshots>
				<enabled>true</enabled>
			</snapshots>
		</pluginRepository>
		<pluginRepository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
			<snapshots>
				<enabled>false</enabled>
			</snapshots>
		</pluginRepository>
	</pluginRepositories>


</project>

/src/main/java/com/in28minutes/mockito/mockitodemo/DataService.java

package com.in28minutes.mockito.mockitodemo;

public interface DataService {
	int[] retrieveAllData();
}

/src/main/java/com/in28minutes/mockito/mockitodemo/MockitoDemoApplication.java

package com.in28minutes.mockito.mockitodemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MockitoDemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(MockitoDemoApplication.class, args);
	}
}

/src/main/java/com/in28minutes/mockito/mockitodemo/SomeBusinessImpl.java

package com.in28minutes.mockito.mockitodemo;

public class SomeBusinessImpl {
	private DataService dataService;

	public SomeBusinessImpl(DataService dataService) {
		super();
		this.dataService = dataService;
	}

	int findTheGreatestFromAllData() {
		int[] data = dataService.retrieveAllData();
		int greatest = Integer.MIN_VALUE;

		for (int value : data) {
			if (value > greatest) {
				greatest = value;
			}
		}
		return greatest;
	}
}

/src/main/resources/application.properties

/src/test/java/com/in28minutes/mockito/mockitodemo/ListTest.java

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import java.util.List;

import org.junit.Test;
import org.mockito.Mockito;

public class ListTest {

	@Test
	public void testSize() {
		List listMock = mock(List.class);
		when(listMock.size()).thenReturn(10);
		assertEquals(10, listMock.size());
		assertEquals(10, listMock.size());
	}

	@Test
	public void testSize_multipleReturns() {
		List listMock = mock(List.class);
		when(listMock.size()).thenReturn(10).thenReturn(20);
		assertEquals(10, listMock.size());
		assertEquals(20, listMock.size());
		assertEquals(20, listMock.size());
	}

	@Test
	public void testGet_SpecificParameter() {
		List listMock = mock(List.class);
		when(listMock.get(0)).thenReturn("SomeString");
		assertEquals("SomeString", listMock.get(0));
		assertEquals(null, listMock.get(1));
	}

	@Test
	public void testGet_GenericParameter() {
		List listMock = mock(List.class);
		when(listMock.get(Mockito.anyInt())).thenReturn("SomeString");
		assertEquals("SomeString", listMock.get(0));
		assertEquals("SomeString", listMock.get(1));
	}
}

/src/test/java/com/in28minutes/mockito/mockitodemo/MockitoDemoApplicationTests.java

package com.in28minutes.mockito.mockitodemo;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MockitoDemoApplicationTests {

	@Test
	public void contextLoads() {
	}

}

/src/test/java/com/in28minutes/mockito/mockitodemo/SomeBusinessMockAnnotationsTest.java

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.when;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.MockitoJUnitRunner;

@RunWith(MockitoJUnitRunner.class)
public class SomeBusinessMockAnnotationsTest {

	@Mock
	DataService dataServiceMock;

	@InjectMocks
	SomeBusinessImpl businessImpl;

	@Test
	public void testFindTheGreatestFromAllData() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 3 });
		assertEquals(24, businessImpl.findTheGreatestFromAllData());
	}

	@Test
	public void testFindTheGreatestFromAllData_ForOneValue() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 15 });
		assertEquals(15, businessImpl.findTheGreatestFromAllData());
	}

	@Test
	public void testFindTheGreatestFromAllData_NoValues() {
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] {});
		assertEquals(Integer.MIN_VALUE, businessImpl.findTheGreatestFromAllData());
	}
}

/src/test/java/com/in28minutes/mockito/mockitodemo/SomeBusinessMockTest.java

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import org.junit.Test;

public class SomeBusinessMockTest {

	@Test
	public void testFindTheGreatestFromAllData() {
		DataService dataServiceMock = mock(DataService.class);
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 24, 15, 3 });
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(dataServiceMock);
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(24, result);
	}

	@Test
	public void testFindTheGreatestFromAllData_ForOneValue() {
		DataService dataServiceMock = mock(DataService.class);
		when(dataServiceMock.retrieveAllData()).thenReturn(new int[] { 15 });
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(dataServiceMock);
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(15, result);
	}

}

/src/test/java/com/in28minutes/mockito/mockitodemo/SomeBusinessStubTest.java

package com.in28minutes.mockito.mockitodemo;

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class SomeBusinessStubTest {
	@Test
	public void testFindTheGreatestFromAllData() {
		SomeBusinessImpl businessImpl = new SomeBusinessImpl(new DataServiceStub());
		int result = businessImpl.findTheGreatestFromAllData();
		assertEquals(24, result);

	}

}

class DataServiceStub implements DataService {
	@Override
	public int[] retrieveAllData() {
		return new int[] { 24, 6, 15 };
	}
}

Related Posts

Docker Tutorial for Beginners - with Java and Spring Boot

Learn about Docker - What is Docker? Why Is Docker Popular? How to create Docker Image for a Java Spring Boot App?

Devops Tutorial | DevOps with Docker, Kubernetes and Azure DevOps

What is DevOps? How is it different from Agile? What are the popular DevOps Tools? What is the role of Docker, Kubernetes and Azure DevOps in DevOps. Let's get started with a simple usecase.

Deploy Java Spring Boot Applications to AWS, Azure, GCP with Docker and Kubernetes

In this article, we focus our attention on the cloud. How to learn the cloud and deploy Java Spring Boot Applications to AWS, Azure, GCP with Docker and Kubernetes?

Spring Boot Tutorials for Beginners

At in28Minutes, we are creating a number of tutorials with videos, articles & courses on Spring Boot for Beginners and Experienced Developers. This resources will help you learn and gain expertise at Spring Boot.

Microservices with Spring Boot and Java - Part 1 - Getting Started

Let's learn the basics of microservices and microservices architectures. We will also start looking at a basic implementation of a microservice with Spring Boot. We will create a couple of microservices and get them to talk to each other using Eureka Naming Server and Ribbon for Client Side Load Balancing. In part 1 of this series, lets get introduced to the concept of microservices and understand how to create great microservices with Spring Boot and Spring Cloud.

20+ Spring Boot Projects with Code Examples

At in28Minutes, we have created more than 20 projects with code examples on Github. We have 50+ articles explaining these projects. These code examples will you learn and gain expertise at Spring Boot.

REST API Best Practices - With Design Examples from Java and Spring Web Services

Designing Great REST API is important to have great microservices. How do you design your REST API? What are the best practices?

Index - 500+ Videos

At in28Minutes, we are creating a number of tutorials with videos, articles & courses on Spring Boot for Beginners and Experienced Developers. Here's a list of video tutorials and courses for you

Creating Spring Boot and React Java Full Stack Application with Maven

This guide helps you create a Java full stack application with all the CRUD (Create, Read, Update and Delete) features using React as Frontend framework and Spring Boot as the backend REST API. We use Maven as the build tool.

Creating a SOAP Web Service with Spring Boot Starter Web Services

Let's learn how to create a SOAP Web Service with Spring Boot Starter Web Services. We will take a Contract First approach by definining an XSD and exposing a WSDL from it.

FREE COURSES



in28Minutes Best Selling Udemy Courses

Image Image Image Image Image Image Image Image Image

450,000 Learners are pursuing our 31 amazing courses and 6 Learning Paths. Start Now!

Join 450,000 Learners and 30+ Amazing Courses

LEARN DEVOPS - 200+ VIDEOS - Master DevOps with Docker, Kubernetes and Azure DevOps

350,000 Learners are learning everyday with our Best Selling Courses : Spring Boot Microservices, Spring, Spring Boot, Web Services, Hibernate, Full Stack React, Full Stack Angular, Python, Spring Interview Guide, Java Interview, Java Functional Programming, AWS, Docker, Kubernetes, PCF, AWS Fargate and Azure

85,000 Subscribers are learning from our Free Videos on YouTube : JSP Servlets, Spring, Spring Boot, Spring MVC, Hibernate, Eclipse, Maven, JUnit, Mockito, Full Stack - React, Full Stack - Angular, Docker, Kubernetes, AWS, AWS Fargate, PCF and Azure

Here are the recommend articles to read next : Spring Interview Questions, Spring Boot Interview Questions, Microservices, Hibernate, Spring Security, REST API with Spring Boot, Full Stack with React, SOAP Web Services, Exception Handling, Embedded Servers, Spring Data Rest, Spring vs Spring MVC vs Spring Boot, Building Web Application and Spring Data JPA.

You can checkout all our 100+ articles here - All Articles.

Do not know where to start your learning journey? Check out our amazing learning paths:
Learning Path 01 - Spring and Spring Boot Web Applications and API Developer,
Learning Path 02 - Full Stack Developer with Spring Boot, React & Angular,
Learning Path 03 - Cloud Microservices Developer with Docker and Kubernetes,
Learning Path 04 - Learn Cloud with Spring Boot, AWS, Azure and PCF and
Learning Path 05 - Learn AWS with Microservices, Docker and Kubernetes

Subscribe