How to Use JUnit on VS Code

Introduction

JUnit is one of the most popular Java application testing frameworks. JUnit enables developers to create unit tests for their code to guarantee its correctness. You may wonder how to use JUnit to test Java when using Visual Studio Code (VS Code) as an IDE. The following instructions will lead you through the process of installing, setting up, and employing JUnit in VS Code.

Prerequisites

Prior to starting, ensure that you have the following installed on your machine:

Java Development Kit (JDK) – JUnit needs Java to execute. Download and install the current release of JDK from Oracle or OpenJDK.

Visual Studio Code – If you haven't installed VS Code, download it here.

Java Extensions for VS Code – Install the required Java extensions to provide Java development support for VS Code.

Step 1: Install Java Extensions in VS Code

To run JUnit on VS Code, you must install some key Java extensions.

Open VS Code and navigate to the Extensions view (Ctrl + Shift + X).

Find "Java Extension Pack" and install it. This pack contains:

Language Support for Java™ by Red Hat

Debugger for Java

Maven for Java

Test Runner for Java

Restart VS Code to set up all extensions correctly.

Step 2: Create a Java Project

You must set up a Java project in which you will execute and test your code.

Open VS Code and navigate to View > Command Palette (Ctrl + Shift + P).

Enter "Java: Create Java Project" and select it.

Select "No Build Tools" or "Maven" (if you will be using dependencies).

Choose a folder in which to save your project and provide a name.

Open the freshly created project in VS Code.

Step 3: Add JUnit Dependency

If you are using Maven, add the following JUnit dependency to your pom.xml file.

<dependencies>

    <dependency>

        <groupId>org.junit.jupiter</groupId>

        <artifactId>junit-jupiter-api</artifactId>

        <version>5.9.1</version>

        <scope>test</scope>

    </dependency>

    <dependency>

        <groupId>org.junit.jupiter</groupId>

        <artifactId>junit-jupiter-engine</artifactId>

        <version>5.9.1</version>

    </dependency>

</dependencies>

If you are not using Maven, download the JUnit .jar files from JUnit’s official site and manually add them to your project's classpath.

Step 4: Write a JUnit Test

Now, create a test class to validate your Java code.

Inside the src/test/java folder (create it if it doesn’t exist), create a new file called CalculatorTest.java.

Write the following test code:

import static org.junit.jupiter.api.Assertions.*;

import org.junit.jupiter.api.Test;

class Calculator {

    public int add(int a, int b) {

        return a + b;

    }

}

public class CalculatorTest {

    @Test

    void testAddition() {

        Calculator calculator = new Calculator();

        assertEquals(5, calculator.add(2, 3));

    }

}

Step 5: Execute JUnit Tests in VS Code

To execute the test, do the following:

Open the file CalculatorTest.java.

Click the Run button to the left of the test method or right-click on the file and choose Run Test.

Alternatively, navigate to the Test Explorer (View > Test) and view all identified test cases and run them.

The results of the test will display in the "Test Results" window in VS Code.

Step 6: Debug JUnit Tests

If a test fails, you might need to debug it. Here are the steps:

Open the test file and place breakpoints by clicking beside the line numbers

Right-click the test method and choose Debug Test

Utilize the Debug Console to step through the code and examine variables.

Conclusion

Working with JUnit in VS Code is easy once you have the necessary extensions and dependencies in place. By working through the steps of this guide, you can write, execute, and debug unit tests in VS Code with ease. This keeps your Java code stable and of high quality.

With JUnit as part of your workflow, you're able to detect bugs early and develop stable Java applications. Happy coding!