JUnit 5 Made Easy

JUnit 5 is a powerful testing framework for Java developers, allowing you to write and run repeatable, automated tests for your code. With its clear and expressive syntax, JUnit 5 makes it easy to write tests for a wide range of scenarios and use cases, from simple unit tests to complex integration tests. In this beginner’s tutorial, we’ll cover the basics of JUnit 5 and walk through the steps of writing and running your first test.

Setting up a JUnit 5 project

Firstly, we will add a simple Calculator Class that contains a method to sum two int values:

public class Calculator {

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

}

Next, you’ll want to create a new class file in your test directory. Typically you can name this Class after the class you want to test with the Test suffix. Therefore, add the following CalculatorTest Class:

package com.example.project;

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

import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvSource;

class CalculatorTests {

    @Test
    @DisplayName("1 + 1 = 2")
    void addTwoNumbers() {
        Calculator calculator = new Calculator();
        assertEquals(2, calculator.add(1, 1), "1 + 1 should equal 2");
    }

    @ParameterizedTest(name = "{0} + {1} = {2}")
    @CsvSource({
            "0,    1,   1",
            "1,    2,   3",
            "49,  51, 100",
            "1,  100, 101"
    })
    void addParams(int first, int second, int expectedResult) {
        Calculator calculator = new Calculator();
        assertEquals(expectedResult, calculator.add(first, second),
                () -> first + " + " + second + " should equal " + expectedResult);
    }
}

To run a JUnit Test, we need to decorate our methods with the @org.junit.jupiter.api.Test annotation.

• The method addtwoNumbers tests a sum of two Integers. It uses the @DisplayName annotation to declare a custom display name for the test method.
• The method addParams is a @ParameterizedTest . Parameterized tests make it possible to run the same test multiple times with different arguments.

After adding the Test Class, check that your Project has the following structure:

Building JUnit 5 applications

Bext, we will configure the pom.xml to build the JUnit 5 project. For this purpose, you should include the following dependencies in your pom.xml:

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.junit</groupId>
            <artifactId>junit-bom</artifactId>
            <version>5.10.1</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

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

At the time of writing (December 2023) the latest version of JUnit Jupiter is 5.10.1.

On the other hand, Gradle users can use the following build.gradle:

plugins {
    id 'java'
    id 'eclipse' // optional (to generate Eclipse project files)
    id 'idea' // optional (to generate IntelliJ IDEA project files)
}

repositories {
    mavenCentral()
}

dependencies {
    testImplementation(platform('org.junit:junit-bom:5.7.2'))
    testImplementation('org.junit.jupiter:junit-jupiter')
}

test {
    useJUnitPlatform()
    testLogging {
        events "passed", "skipped", "failed"
    }
}

Finally, run the above test from the Command Line or from your IDE:

As you can see, all assertion were verified so test passed. Also notice that the first Test contains the @DisplayName attribute from our method (“1 + 1 = 2”).

The source code for this tutorial is available here: https://github.com/fmarchioni/mastertheboss/tree/master/test/junit5-jupiter

Summary:

• JUnit is a framework which supports several annotations to identify a method which contains a test.
• JUnit provides an annotation called @Test, which tells the JUnit that the public void method in which it is used can run as a test case.
• JUnit can be easily be plugged in your IDE: check this tutorial as an example: Getting started with JUnit and IntelliJ Idea