java

Java

Java testing with JUnit5, Mockito and AssertJ

• Show me the code
  • Implementation
  • Test
• Run this project using 🐳 docker
• Run this project locally

Show me the code

Implementation

1. Create HelloMessage class in HelloMessage.java:

public class HelloMessage {
  public String getText() {
    return "Hello World!";
  }
}

We can create it as a class as Mockito is able to mock final classes.

2. Same way create HelloConsole class in HelloConsole.java:

public class HelloConsole {
  public void print(String text) {
    System.out.println(text);
  }
}

3. Create HelloApp class in HelloApp.java:

public class HelloApp {

  private final HelloMessage message;
  private final HelloConsole console;

  public HelloApp(HelloMessage message, HelloConsole console) {
    this.message = message;
    this.console = console;
  }

  public void printHello() {
    console.print(message.getText());
  }
}

4. Create main class in Main.java that wraps it all together:

public class Main {

  public static void main(String[] args) {
    var message = new HelloMessage();
    var console = new HelloConsole();
    var app = new HelloApp(message, console);
    app.printHello();
  }
}

Test

Following JUnit5 > Writing Tests, Mockito > Stubbing and AssertJ > Core assertions guide guides ...

1. Test HelloMessage in HelloMessageTest.java:

@Test
void shouldReturnHelloWorld() {
  var message = new HelloMessage();
  assertThat(message.getText()).isEqualTo("Hello World!");
}

2. Test HelloApp in HelloAppTest.java:

@Test
void shouldPrintHelloMessage() {

  var messageText = "Hello Test!";

  // 2.1 Create a mock of HelloMessage
  var message = mock(HelloMessage.class);
  // 2.2 Return "Hello Test!" whenever getText() is called
  when(message.getText()).thenReturn(messageText);

  // 2.2 Create a mock of HelloConsole
  var console = mock(HelloConsole.class);

  // 2.3 Create a HelloApp, the one we want to test, passing the mocks
  var app = new HelloApp(message, console);
  // 2.4 Execute the method we want to test
  app.printHello();

  // 2.5 Verify HelloConsole mock print() method
  // has been called once with "Hello Test!"
  verify(console).print(messageText);
}

3. Test output should look like:

> Task :test

HelloAppTest > shouldPrintHelloMessage() PASSED

HelloMessageTest > shouldReturnHelloWorld() PASSED

BUILD SUCCESSFUL in 2s

Run this project using 🐳 docker

• Execute ./docker-run.sh
• Once inside the container:
  • Test with ./gradlew test --rerun-tasks
  • Run with ./gradlew run

Run this project locally

Pre-requisites

• Install Java and Gradle manually or ...
  • Install SdkMan and ...
    • List available versions executing sdk list java and sdk list gradle
    • Install Java executing sdk install java 21-tem
    • Install Gradle executing sdk install grade 8.4

Run locally

• Test with ./gradlew test --rerun-tasks
• Run with ./gradlew run

Create project from scratch

• Create project using gradle init --type java-application --dsl kotlin --test-framework junit-jupiter
• Add Mockito and AssertJ dependencies in build.gradle.kts:

  dependencies {
    testImplementation("org.mockito:mockito-core:x.x.x")
    testImplementation("org.assertj:assertj-core:x.x.x")
  }