How To Run Java Unit Tests In VS Code: A Step-by-Step Guide

Unit testing is a crucial practice for Java developers to ensure code reliability and maintainability. Visual Studio Code (VS Code), known for its versatility, can be an effective environment for running and debugging Java unit tests. In this guide, we’ll walk through the essential steps for setting up and running Java unit tests in VS Code.

Step 1: Install Necessary Extensions

To work with Java in VS Code and effectively run unit tests, you need to install specific extensions. Here’s how to set up your environment:

1. Extension Pack for Java: This pack includes essential tools like Language Support for Java, Debugger, Maven and Gradle runtimes.

• Go to the Extensions View (Ctrl + Shift + X or Cmd + Shift + X on macOS).
• Search for “Extension Pack for Java” and click Install.

1. Test Runner for Java: This extension is necessary to run and debug Java tests.

• Search for “Test Runner for Java” in the Extensions View.
• Click Install.

Step 2: Set Up Your Java Project

Ensure you have a Java project set up with a folder structure that supports unit tests. If not, create a simple Maven or Gradle project:

• Maven: Run mvn archetype:generate from the command line and choose a suitable archetype.
• Gradle: Run gradle init and follow the prompts to create a basic Java project.

Place your unit tests in the src/test/java directory, following the standard convention.

Step 3: Write Your Unit Test

Create a test class in your src/test/java directory. Ensure you use a testing framework like JUnit. Here’s an example:

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

public class ExampleTest {
    @Test
    public void testAddition() {
        int result = 2 + 3;
        assertEquals(5, result);
    }
}

Optional: Generate a Unit Test Class with a Hotkey

Navigate to the Java class you’d like to test, and use the Code Actions feature to generate the Unit Test class:

• Windows/Linux: Highlight the class or method, and press Ctrl + .
• macOS: Press Cmd + .

Select “Source Actions” -> “Generate Unit Test” and VS Code will generate a Unit test class in the /src/main/test folder

Additionally, extensions such as Test Generator can be installed to provide more automated test creation features.

Step 5: Run Your Unit Tests

With the Test Runner for Java extension installed, running tests is straightforward:

1. Open the test file in VS Code.
2. You will see a Run Test and Debug Test button appear next to each test method.
3. Click the Run Test button to execute the test.

Alternatively, you can:

• Right-click on the file in the Explorer panel and select Run Tests.
• Run all tests in the project by opening the Testing side panel (Ctrl + Shift + = or Cmd + Shift + = on macOS) and clicking Run All Tests.

Step 6: View Test Results

VS Code displays test results in the Testing panel, which shows detailed information about each test’s outcome:

1. Enable the Testing Panel: Open the Testing side panel by pressing Ctrl + Shift + = (Windows/Linux) or Cmd + Shift + = (macOS). If the panel is not visible, go to View > Testing.
2. Test Status: Each test will be marked with a green checkmark for success or a red X for failure.
3. Detailed Output: Click on a test result to view more information, including stack traces and error messages.

Additional Views:

• Test Explorer: The Testing panel provides an overview of all tests in the project, showing their hierarchy and status.
• Terminal Output: When running tests via the command line, results are also displayed in the Terminal.

Step 7: Debug Your Unit Tests

Debugging is as important as running the tests, especially when something goes wrong. To debug:

1. Click the Debug Test button next to the test method.
2. The debugger will start, and you can set breakpoints by clicking in the left margin of the code editor.
3. Use the Debug Toolbar to step over, step into, or continue execution as needed.

Key Debugging Tips:

• Watch Expressions: Use the Variables panel to inspect variable values.
• Call Stack: Check the Call Stack to trace the execution path.
• Breakpoints: Add conditional breakpoints by right-clicking a breakpoint and selecting Edit Breakpoint.

Final Thoughts

Running and debugging Java unit tests in VS Code is seamless with the right extensions. With this setup, you can ensure your code is robust and catch issues early in the development cycle.

Happy coding and testing!