First JUnit Test

 

Here's a step-by-step guide to writing your first JUnit test in Eclipse, using JUnit 5 (also known as JUnit Jupiter).

Step 1: Set Up Eclipse Project

• Open Eclipse.
• Go to File → New → Java Project.
• Name the project, example: JUnitDemo.
• Click Finish.

Step 2: Add JUnit 5 Library

• Right-click the project → Build Path → Add Libraries.
• Select JUnit → Click Next.
• Choose JUnit 5 → Click Finish.

If JUnit 5 is not available, you may need to download JUnit 5 from Maven/Gradle or manually add its .jar files.

Step 3: Create a Class to Test

Create a Java class that has some logic you want to test.

// File: Calculator.java
public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

Step 4: Create a JUnit Test Class

• Right-click on the src folder → New → JUnit Test Case.
• Name it CalculatorTest.
• Select JUnit 5 as the version.
• Click Finish.

Step 5: Write Your First Test

// File: CalculatorTest.java
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class CalculatorTest {

    @Test
    public void testAddition() {
        Calculator calc = new Calculator();
        int result = calc.add(10, 5);
        assertEquals(15, result, "10 + 5 should equal 15");
    }
}

Step 6: Run the Test

• Right-click on CalculatorTest.java.

• Select Run As → JUnit Test.

JUnit 5 Key Annotations

Annotation	Description
@Test	Marks a method as a test method
@BeforeEach	Runs before each test method
@AfterEach	Runs after each test method
@BeforeAll	Runs once before all test methods (static)
@AfterAll	Runs once after all test methods (static)
@Disabled	Disables a test temporarily