Mockito is the most popular mocking framework in Java.
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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.
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
- Choose
- 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
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>2.3.1.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>
<maven-jar-plugin.version>3.1.1</maven-jar-plugin.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 };
}
}