Introduction of JUnit

  

JUnit is a unit testing framework for the Java programming language. It plays a crucial role in test-driven development (TDD) and is used to write and run repeatable tests. JUnit belongs to the family of XUnit frameworks, and it is one of the most popular testing libraries in Java.

Key Features of JUnit

Feature	Description
Annotations	Uses annotations like @Test, @BeforeEach, @AfterEach, @BeforeAll, @AfterAll, etc.
Assertions	Provides assertion methods like assertEquals(), assertTrue(), etc.
Test Runner	JUnit provides test runners to run test classes individually or as part of a suite.
Integration	Easily integrates with build tools like Maven/Gradle and IDEs like Eclipse, IntelliJ.

Common JUnit 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 (must be static)
@AfterAll	Runs once after all test methods (must be static)
@Disabled	Skips a test method or class

Simple Example of JUnit (JUnit 5)

Java Class to Test (Calculator.java)

public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }

    public int subtract(int a, int b) {
        return a - b;
    }
}

Test Class (CalculatorTest.java)

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

public class CalculatorTest {

    Calculator calculator;

    @BeforeEach
    void setUp() {
        calculator = new Calculator();
        System.out.println("Before Each Test");
    }

    @AfterEach
    void tearDown() {
        System.out.println("After Each Test");
    }

    @Test
    void testAddition() {
        assertEquals(5, calculator.add(2, 3), "2 + 3 should equal 5");
    }

    @Test
    void testSubtraction() {
        assertEquals(1, calculator.subtract(3, 2), "3 - 2 should equal 1");
    }
}

How to Run JUnit Tests

You can run JUnit tests in several ways:

• From IDE like Eclipse/IntelliJ (Right-click → Run As → JUnit Test)

• Using build tools like Maven/Gradle

• Command line (using javac and java with JUnit jars)

Maven Dependency for JUnit 5

If you're using Maven:

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>

Important Points:

• JUnit helps automate and structure your unit tests.

• It promotes cleaner code and faster debugging.

• Easily integrates with CI/CD tools, Maven, and IDEs.

• Essential for TDD and Agile methodologies.