Mockito adds functionality to a mock object using the when() method. Take a look at the following code snippet.
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MyUtils mock = mock(MyUtils.class); when(mock.add(10, 40)).thenReturn(50); doReturn(50).when(mock).add(10, 40); |
Here we are instructing the Mockito to provide or give a behavior of adding 10 and 40 to the add method of MyUtils and as a result, to return the value of 50
Let’s try to understand the above concept using a demo project
pom.xml
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<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 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.kkjavatutorials</groupId> <artifactId>MockitoAddingBehaviorExample</artifactId> <version>0.0.1-SNAPSHOT</version> <properties> <maven.compiler.target>8</maven.compiler.target> <maven.compiler.source>8</maven.compiler.source> </properties> <dependencies> <dependency> <groupId>org.mockito</groupId> <artifactId>mockito-junit-jupiter</artifactId> <version>3.5.7</version> <scope>test</scope> </dependency> </dependencies> </project> |
MyUtils.java
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package com.kkjavatutorials; public interface MyUtils { public abstract int add(int n1,int n2); public abstract int multiply(int n1,int n2); } |
MyUtilsTest.java
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package com.kkjavatutorials; import org.junit.jupiter.api.Test; import static org.junit.jupiter.api.Assertions.assertEquals; import static org.mockito.Mockito.*; import java.util.List; public class MyUtilsTest { @Test void addMockitoSimpleBehaviorTest1() { MyUtils mock = mock(MyUtils.class); when(mock.add(10, 40)).thenReturn(50); doReturn(50).when(mock).add(10, 40); assertEquals(50, mock.add(10, 40)); assertEquals(50, mock.add(10, 40)); } @Test void addMockitoSimpleBehaviorTest2() { MyUtils mock = mock(MyUtils.class); when(mock.multiply(20, 20)).thenReturn(400); assertEquals(400, mock.multiply(20, 20)); } @Test void addMockitoconsecutiveMethodCallsTest() { MyUtils mock = mock(MyUtils.class); when(mock.add(anyInt(), anyInt())).thenReturn(60,70,90); assertEquals(60, mock.add(20, 40)); assertEquals(70, mock.add(20, 50)); assertEquals(90, mock.add(50, 40)); } @Test void addMockitoSpyBehaviorTest() { List<String> spy = spy(List.class); doReturn(20).when(spy).size(); assertEquals(20, spy.size()); } @Test void addMockitoBehaviorWithCustomAnswerTest() { List mock = mock(List.class); doAnswer(answer ->"My Answer").when(mock).get(anyInt()); assertEquals("My Answer", mock.get(2)); } } |
The Output of the above project:
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That’s all about Adding behavior to mocked object in Mockito
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