This is an article forJava Unit Testing with JUnit Example.

You can also check this tutorial in the following video:

1. Introduction

Java unit testing is a software testing where methods and classes are tested.JUnit is a unit testing framework for the Java programming language which provides a way to test the application as many as you want. Unit testing usually includes the following steps:

1. define a test
2. create an instance of the testing class
3. prepare the test data
4. execute a test
5. verify the testing results
6. report the testing results

JUnit supports step 1 via@Test annotation, step 4 via@RunWith annotation, and step 5 via assertion API. In this example, I will create a multi-module maven project to demonstrate how to utilize the JUnit framework to create a test class.

2. Technologies Used

The example code in this article was built and run using:

• Java 11
• Maven 3.3.9
• Eclipse Oxygen
• JUnit (4 and 5)

3. Maven Multi-Modules Project

JUnit 5 was released in 2017. It is not backwards compatible withJUnit 4 which released in 2006. In this step, I will demonstrate both JUnit 4 and JUnit 5 in a three-module Maven project:

• common – includes a main class –SomeClass.
• JUnit4-demo – testsSomeClass with JUnit 4.
• JUnit5-demo – testsSomeClass with JUnit 5.

3.1 Parent POM

Parentpom.xml includes three modules and two common build plug-ins:

• maven-compiler-plugin – defines the Java 11 for the compiler
• maven-surefire-plugin – defines the JUnit report plug-in

pom.xml

<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>jcg.zheng.demo</groupId><artifactId>junit-demo</artifactId><version>0.0.1-SNAPSHOT</version><packaging>pom</packaging><name>junit-demo</name><url>http://maven.apache.org</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><description>parent project for junit demo</description><modules><module>common</module><module>junit4-demo</module><module>junit5-demo</module></modules><build><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.8.0</version><configuration><release>11</release></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-surefire-plugin</artifactId><version>3.0.0-M3</version></plugin></plugins></build></project>

Execute mvn clean install command and capture the output here:

[INFO] Reactor Summary for junit-demo 0.0.1-SNAPSHOT:[INFO][INFO] junit-demo ......................................... SUCCESS [  2.287 s][INFO] comon .............................................. SUCCESS [ 10.295 s][INFO] junit4-demo ........................................ SUCCESS [  6.631 s][INFO] junit5-demo ........................................ SUCCESS [  6.191 s][INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time:  26.052 s[INFO] Finished at: 2020-03-30T20:46:54-05:00[INFO] ------------------------------------------------------------------------

4. Common Module

In this step, I will create a common module which contains a main class. The main class will be tested at both JUnit 4 and JUnit 5 at its respective module.

4.1 POM

Thecommon module’spom.xml is defined as the following:

pom.xml

<?xml version="1.0"?><projectxsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><modelVersion>4.0.0</modelVersion><parent><groupId>jcg.zheng.demo</groupId><artifactId>junit-demo</artifactId><version>0.0.1-SNAPSHOT</version></parent><artifactId>common</artifactId><name>comon</name><url>http://maven.apache.org</url></project>

4.2 SomeClass

In this step, I will createSomeClass which has the following methods:

• doubleANumber – return an integer number by multiplying two.
• returnABoolean – return aboolean value based on the input string value.
• voidFoo – does not return anything and throws an exception when receiving a bad argument.

SomeClass.java

package jcg.zheng.demo;public class SomeClass { public int doubleANumber(int num) {return num * 2;}public boolean returnABoolean(String inputData) {if ("Save".equalsIgnoreCase(inputData)) {return true;} else {return false;}}public void voidFoo(String inputData) {if ("Ok".equalsIgnoreCase(inputData)) {System.out.println("doing something.");;} else {throw new IllegalArgumentException("Bad argument:" + inputData);}}}

5. JUnit 4 Module

JUnit 4 was first released in 2006. It only has one jar and requires JDK 5 or higher version.

5.1 POM

TheJUnit4-demo module’spom.xml and depends on JUnit 4 and thecommon module.

In this step, I will create a JUnit 4 test class to testSomeClass.

pom.xml

<?xml version="1.0"?><projectxsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><modelVersion>4.0.0</modelVersion><parent><groupId>jcg.zheng.demo</groupId><artifactId>junit-demo</artifactId><version>0.0.1-SNAPSHOT</version></parent><artifactId>junit4-demo</artifactId><name>junit4-demo</name><url>http://maven.apache.org</url><properties><junit.version>4.12</junit.version></properties><dependencies><dependency><groupId>jcg.zheng.demo</groupId><artifactId>common</artifactId><version>0.0.1-SNAPSHOT</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>${junit.version}</version><scope>test</scope></dependency></dependencies></project>

5.2 SomeClassTest

In this step, I will create aSomeClassTest class in JUnit 4.

• Define a test with@org.junit.Test
• Print out a test name with a@org.junit.Rule on aorg.junit.rules.TestName class
• Setup the test before each tests with@org.junit.Before
• Ignore a test with@org.junit.Ignore
• Set a test with a timeout limitation
• Set a test with an expected exception
• Verify the testing result with the expected value with a static classorg.junit.Assert

SomeClassTest.java

package jcg.zheng.demo.junit4;import static org.junit.Assert.assertEquals;import static org.junit.Assert.assertFalse;import static org.junit.Assert.assertTrue;import static org.junit.Assert.fail;import org.junit.Before;import org.junit.Ignore;import org.junit.Rule;import org.junit.Test;import org.junit.rules.TestName;import jcg.zheng.demo.SomeClass;public class SomeClassTest {private SomeClass classUnderTest = new SomeClass();@Rulepublic TestName testName = new TestName();@Beforepublic void setup() {classUnderTest = new SomeClass();System.out.println("Start " + testName.getMethodName());}@Testpublic void test_doubleANumber() {assertEquals(6, classUnderTest.doubleANumber(3));}@Ignorepublic void test_not_executed() {fail("It should not executed");}@Testpublic void test_returnBooleanFoo_false() {boolean shouldReturnFalse = classUnderTest.returnABoolean("NA");assertFalse(shouldReturnFalse);}@Testpublic void test_returnBooleanFoo_true() {boolean shouldReturnTrue = classUnderTest.returnABoolean("Save");assertTrue(shouldReturnTrue);}@Testpublic void test_voidFoo() throws IllegalAccessException {try {classUnderTest.voidFoo("OK");} catch (Exception e) {fail("Should not throw exception");}}@Test(expected = IllegalArgumentException.class)public void test_voidFoo_exception() throws IllegalAccessException {classUnderTest.voidFoo("NA");}@Test(timeout = 1)public void test_timeout() {classUnderTest.doubleANumber(9999);}}

• Line 20, 26 – theTestName instance marked by@Rule can access the test name.
• Line 23 – the method marked with@Before will be invoked before executing each test.
• Line 29 –@Test marks a method as a test. It will be executed by the JUnit default runner.
• Line 34 – JUnit runner will ignore test tests which marks with@Ignore.
• Line 31, 42, 48 – invokesassertFalse,assertTrue,assertEquals to verify the test results to the expected value.
• Line 60 – catch the expected exception.
• Line 65 – set up the timeout limit.

Output

[INFO] -------------------------------------------------------[INFO]  T E S T S[INFO] -------------------------------------------------------[INFO] Running jcg.zheng.demo.junit4.SomeClassTestStart test_voidFoodoing something.Start test_returnBooleanFoo_falseStart test_voidFoo_exceptionStart test_doubleANumberStart test_timeoutStart test_returnBooleanFoo_true[INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.214 s - in jcg.zheng.demo.junit4.SomeClassTest[INFO][INFO] Results:[INFO][INFO] Tests run: 6, Failures: 0, Errors: 0, Skipped: 0

6. JUnit 5 Module

JUnit 5 was first released in 2017. It requires JDK 8 or higher. It includes a collection of three sub-projects: JUnit Jupiter, JUnit Platform, and JUnit Vintage.

6.1 POM

TheJUnit5-demo module’spom.xml depends on JUnit 5 and common modules. Please note that it includes two of JUnit 5 modules:junit-jupiter-engineandjunit-jupiter-api.

In this step, I will create a JUnit 5 test class to testSomeClass.

pom.xml

<?xml version="1.0"?><projectxsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><modelVersion>4.0.0</modelVersion><parent><groupId>jcg.zheng.demo</groupId><artifactId>junit-demo</artifactId><version>0.0.1-SNAPSHOT</version></parent><artifactId>junit5-demo</artifactId><name>junit5-demo</name><url>http://maven.apache.org</url><properties><junit-jupiter.version>5.5.2</junit-jupiter.version></properties><dependencies><dependency><groupId>jcg.zheng.demo</groupId><artifactId>common</artifactId><version>0.0.1-SNAPSHOT</version></dependency> <dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-engine</artifactId><version>${junit-jupiter.version}</version><scope>test</scope></dependency><dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-api</artifactId><version>${junit-jupiter.version}</version><scope>test</scope></dependency></dependencies></project>

6.2 SomeClassTest

In this step, I will create aSomeClassTest class in JUnit 5.

• Define a test with@org.junit.jupiter.api.Test
• Define a display name with@org.junit.jupiter.api.DisplayName
• Print out a test name from@org.junit.jupiter.api.TestInfo
• Setup the test before each tests with@org.junit.jupiter.api.BeforeEach
• Ignore a test with@org.junit.jupiter.api.Disabled
• Set a test with theorg.junit.jupiter.api.assertTimeout method
• Catch an exception with theorg.junit.jupiter.api.assertThrow method
• Verify the testing result with the expected value with astatic class:org.junit.jupiter.api.Assertions

SomeClassTest.java

package jcg.zheng.demo.junit5;import static org.junit.jupiter.api.Assertions.assertEquals;import static org.junit.jupiter.api.Assertions.assertFalse;import static org.junit.jupiter.api.Assertions.assertThrows;import static org.junit.jupiter.api.Assertions.assertTimeout;import static org.junit.jupiter.api.Assertions.assertTrue;import static org.junit.jupiter.api.Assertions.fail;import java.time.Duration;import org.junit.jupiter.api.BeforeEach;import org.junit.jupiter.api.Disabled;import org.junit.jupiter.api.DisplayName;import org.junit.jupiter.api.RepeatedTest;import org.junit.jupiter.api.Test;import org.junit.jupiter.api.TestInfo;import org.junit.jupiter.api.TestReporter;import jcg.zheng.demo.SomeClass;public class SomeClassTest {private SomeClass classUnderTest;private TestInfo testInfo;private TestReporter testReporter;@BeforeEachpublic void setup(TestInfo testInfo, TestReporter terstReporter ) {this.testInfo = testInfo;this.testReporter = terstReporter;classUnderTest = new SomeClass();}@RepeatedTest(5)public void test_doubleANumber() {assertEquals(6, classUnderTest.doubleANumber(3), "it should return 6");}@Disabledpublic void test_not_executed() {fail("It should not executed");}@Test@DisplayName("It should return false when input data isn't Save")public void test_returnBooleanFoo_false() {boolean shouldReturnFalse = classUnderTest.returnABoolean("NA");assertFalse(shouldReturnFalse);}@Test@DisplayName("It should return true when input data is Save")public void test_returnBooleanFoo_true() {boolean shouldReturnTrue = classUnderTest.returnABoolean("Save");assertTrue(shouldReturnTrue);testReporter.publishEntry(testInfo.getDisplayName());}@Testpublic void test_voidFoo() throws IllegalAccessException { try {classUnderTest.voidFoo("OK");} catch (Exception e) {fail("Should not throw exception");}}@Testpublic void test_voidFoo_exception() throws IllegalAccessException {assertThrows(IllegalArgumentException.class, () -> {classUnderTest.voidFoo("NA");});}@Testpublic void test_timeout() {assertTimeout(Duration.ofMillis(1), ()-> classUnderTest.doubleANumber(1000));}}

• Line 28 –@BeforeEach marks the method to be executed for each test.
• Line 29 – can injectTestInfo andTestReporter from Junit framework.
• Line 35 –@RepeatedTest annotation is a new annotation in Junit 5 which executes the test repeatedly.
• Line 40 –@Disabled annotation replaces the@Ignore annotation in Junit 4.
• Line 45 –@Test inorg.junit.jupiter.api package marks a test.
• Line 46 –@DisplayName is a new annotation which names the test with a more meaningful name.
• Line 72 –assertThrows in JUnit 5 replaces the@Test‘sexpected attribute in Junit 4 .
• Line 80 –assertTimeout in JUnit 5 replaces the@Test‘stimeout attribute in Junit 4 .

Output

[INFO] -------------------------------------------------------[INFO]  T E S T S[INFO] -------------------------------------------------------[INFO] Running jcg.zheng.demo.junit5.SomeClassTestdoing something.[INFO] Tests run: 10, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.254 s - in jcg.zheng.demo.junit5.SomeClassTest[INFO][INFO] Results:[INFO][INFO] Tests run: 10, Failures: 0, Errors: 0, Skipped: 0

In Eclipse IDE, you can see the test with the display name.

7. Summary

In this example, I demonstrated how to write a unit test in JUnit. Here are the major differences between JUnit 4 and JUnit 5:

8. Download the Source Code

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