Sample code for basic mocking and testing with Mockito 3 + JUnit 5

Overview

--Show sample code for basic mocking and testing with Mockito 3 + JUnit 5 --Operation check environment this time: Java 14 (AdoptOpenJDK 14.0.2 + 12) + Gradle 6.5.1 + Mockito 3.4.6 + JUnit 5.6.2 + macOS Catalina

Sample code

Source code list

├── build.gradle
└── src
    ├── main
    │   └── java
    │       ├── Client.java
    │       └── Worker.java
    └── test
        └── java
            └── ClientTest.java

build.gradle

Gradle configuration file for build test execution.

plugins {
  id 'java'
}

repositories {
  jcenter()
}

dependencies {
  //Introduced Junit 5
  // https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter
  testImplementation 'org.junit.jupiter:junit-jupiter:5.6.2'

  //Introduced Mockito 3
  // https://mvnrepository.com/artifact/org.mockito/mockito-core
  testImplementation 'org.mockito:mockito-core:3.4.6'

  //Introducing the JUnit 5 Extension library with Mockito
  // https://mvnrepository.com/artifact/org.mockito/mockito-junit-jupiter
  testImplementation 'org.mockito:mockito-junit-jupiter:3.4.6'
}

test {
  //Settings to use JUnit platform
  useJUnitPlatform()

  //Output settings during testing
  testLogging {
    //Display standard output and standard error output during testing
    showStandardStreams true
    //Output event(TestLogEvent)
    events 'started', 'skipped', 'passed', 'failed'
    //Output settings when an exception occurs(TestExceptionFormat)
    exceptionFormat 'full'
  }
}

src/main/java/Worker.java

The class to be mocked.

public class Worker {

  //Method with argument / return value
  public int ariari(int x) {
    throw new IllegalStateException("Exceptions that seem to occur depending on the environment");
  }

  //Method with no arguments and no return value
  public void nasinasi() {
    throw new IllegalStateException("Exceptions that seem to occur depending on the environment");
  }
}

src/main/java/Client.java

The class to be tested.

public class Client {

  private Worker worker;

  //Call a method with arguments and return values
  public int callAriari(int x) {
    return worker.ariari(x * 2); //Doubled value for Worker#Pass to ariari
  }

  //Call a method with no arguments and no return value
  public int callNasinasi(int x) {
    worker.nasinasi(); // Worker#Call nasinasi
    return x * 2; //Returns a doubled value
  }
}

src/test/java/ClientTest.java

Test class. Mock the Worker class with Mockito 3 and test the Client class with JUnit 5.

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.mockito.Mockito.doNothing;
import static org.mockito.Mockito.doReturn;
import static org.mockito.Mockito.doThrow;

@ExtendWith(MockitoExtension.class) //JUnit 5 extension with Mockito
public class ClientTest {

  //Object to inject mock
  @InjectMocks
  private Client client = new Client();

  //Object to mock
  @Mock
  private Worker mockedWorker;

  @Test
public void with arguments_There is a return value() {
    //Mock behavior: Worker#Returns 6 when 2 is passed to ariari
    doReturn(6).when(mockedWorker).ariari(2);
    //test: Client#Passing 1 to callAriari is a mock worker#Pass 2 to ariari and 6 is returned
    assertEquals(6, client.callAriari(1));
  }

  @Test
public void no arguments_No return value() {
    //Mock behavior: Worker#Do nothing when calling nasinasi
    doNothing().when(mockedWorker).nasinasi();
    //test: Client#Passing 1 to callNasinasi is a mock worker#Run nasinasi and get 2 back
    assertEquals(2, client.callNasinasi(1));
  }

  @Test
public void Exception occurred() {
    //Mock behavior: Worker#Throw an exception when 4 is passed to ariari
    doThrow(new IllegalArgumentException("Mock exception")).when(mockedWorker).ariari(4);
    //test: Client#Passing 2 to callAriari is a mock worker#Passing 4 to ariari throws an exception
    IllegalArgumentException e = assertThrows(IllegalArgumentException.class, () -> client.callAriari(2));
    //test:The exception contains the expected message
    assertEquals("Mock exception", e.getMessage());
  }

  @Test
public void sequential call() {
    //Mock behavior: Worker#Throws an exception twice when 6 is passed to ariari and then returns 18.
    doThrow(new IllegalArgumentException("1st mock exception"))
      .doThrow(new IllegalArgumentException("Second mock exception"))
      .doReturn(18)
      .when(mockedWorker).ariari(6);
    //test: Client#Passing 3 to callAriari is a mock worker#Pass 6 to ariari and throw an exception
    IllegalArgumentException e1 = assertThrows(IllegalArgumentException.class, () -> client.callAriari(3));
    assertEquals("1st mock exception", e1.getMessage());
    //test: Client#Passing 3 to callAriari is a mock worker#Pass 6 to ariari and throw an exception
    IllegalArgumentException e2 = assertThrows(IllegalArgumentException.class, () -> client.callAriari(3));
    assertEquals("Second mock exception", e2.getMessage());
    //test: Client#Passing 3 to callAriari is a mock worker#Pass 6 to ariari and 18 is returned
    assertEquals(18, client.callAriari(3));
  }
}

Test run

An example of running the test task in Gradle.

$ gradle test

> Task :test

ClientTest >No arguments_No return value() STARTED

ClientTest >No arguments_No return value() PASSED

ClientTest >With arguments_There is a return value() STARTED

ClientTest >With arguments_There is a return value() PASSED

ClientTest >Exception occurred() STARTED

ClientTest >Exception occurred() PASSED

ClientTest >Sequential call() STARTED

ClientTest >Sequential call() PASSED

BUILD SUCCESSFUL in 2s
3 actionable tasks: 3 executed

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