How to implement JUnit 5 in Your Maven or Gradle Project: A Step-by-Step Guide for Java Testing

Unit Testing JUnit

Learn how to integrate JUnit 5 in your Maven or Gradle project for efficient Java testing. This guide covers adding dependencies, creating test classes, writing test methods, and running tests in IntelliJ IDEA and Visual Studio Code to ensure robust and error-free code.

Step 1: Create a Simple Java Application
Create a simple Java application, for example, “Copilot Demo,” and select Maven or Gradle as the build system through IntelliJ IDEA or Visual Studio Code.

Step 2: Add JUnit Dependency
For Maven:
Add the following dependency to your pom.xml file inside the <dependencies> tag:

XML
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>5.11.2</version>
<scope>test</scope>
</dependency>

For Gradle:
Add the following dependencies to your build.gradle file:
dependencies {
testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.11.2'
}

Step 3: Create a Test Class
To write tests, create a test class in the src/test/java directory. Follow the package structure of your class under test. For example, if you’re testing a class in src/main/java/org/example/MyClass.java, create your test class in src/test/java/org/example/MyClassTest.java.

Step 4: Write Test Methods
In your test class, write test methods to test the functionality of your classes. Each test method should be annotated with @Test. Here’s an example of a simple test method:

Java
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class MyClassTest {
@Test
public void testMethod() {
MyClass myClass = new MyClass();
assertEquals("Expected result", myClass.methodUnderTest());
}
}

Replace "Expected result" and methodUnderTest() with the expected result and the method you are testing, respectively.

Step 5: Run Tests

In IntelliJ IDEA:
Right-click on the test class or method and select Run 'MyClassTest'. IntelliJ IDEA will execute the tests and display the results in the Run window.

In Visual Studio Code:
Use the Test Explorer to run your tests. You can view the test results in the Test Explorer view, editor gutter, and Test Results panel.

Step 6: View Test Results
In IntelliJ IDEA:
After running the tests, IntelliJ IDEA shows the results in the Run window. You can see which tests passed or failed and debug your code accordingly.
!IntelliJ IDEA Test Results1

In Visual Studio Code:
After running/debugging the test cases, the state of the related test items will be updated in both editor decorations and the Testing Explorer. You can trigger the command Test: Peek Output to peek the results view. 
!Visual Studio Code Test Results2

Conclusion
By following these steps, you can easily integrate JUnit 5 into your Maven or Gradle project, write and run tests to ensure your code behaves as expected. This process helps in maintaining a robust and error-free codebase.