How to write JUnit test cases

According to Statista, Java is the sixth most popular programming language used by software developers globally with a round 33% developers using it. The reliable nature of Java projects makes it necessary to develop a testing framework that is equally efficient as possible. However, the framework must also support automation testing to enable quick production, simple maintenance, handy nature, and reduced time consumption.

If your application is written in Java, the fastest and easiest framework to pick is JUnit. This guide will help you understand JUnit test cases for overall satisfaction before rolling out the product to the end customers.

How to write JUnit Test Cases

The idea behind implementing unit testing is to ensure the proper functioning of individual components and verify their behavior. When testing small chunks of code instead of a larger portion of a project, the objective is to focus on the functionality of a single component rather than the interactions between them. This way you can identify bugs early in the project and make the workflow smooth for the developer.

Among the top Unit Testing Frameworks in Selenium, JUnit is one of the most popular Java Frameworks for Unit Testing with Selenium. It was developed with the sole intention of writing and running repeatable tests and supports test-driven development (TDD).

JUnit tests are written in the same manner as Java projects, however, while writing tests you must be aware of some JUnit annotations. JUnit annotations are blocks of predefined texts provided by the Java API for better structure and readability.

Here is an example of a few frequently used JUnit annotations that come in handy in this tutorial on Java JUnit testing.

1. @Test – to identify the actual test case
2. @Before – to execute some statement before each test case
3. @After – to execute some statement after each test case
4. @Ignores – to ignore some statement during execution of test
5. @BeforeAll – to execute some statement before all the test cases
6. @AfterAll – to execute some statement after all the test cases

JUnit Testing Example

Now, let’s consider a practical example to understand Java Junit testing. This example, will conduct a simple test using JUnit where:

• First assign some value to a string, and
• Then with the help of the assert keyword, checking if the value assigned matches our intended value.

Prerequisite

1. You must have Java jdk installed on your system. To check if Java is installed on your system run the command java –version in the Command prompt. If it is installed, it will display the Java version.
2. Any IDE of your choice. In this example, using Eclipse 2022.

Step 1: Create a Maven project 

To create a Maven project, open Eclipse and then complete the following steps:

a. Click on File option

b. Hover on the New drop-down menu

c. Click on the Project option

d. Select the Maven project option

e. Enter the Group id and Artifact id of your choice and proceed.

f. Your Maven project is created.

Step 2: Add Maven dependencies 

In this step, you have to add some dependencies that will help in achieving JUnit testing. Add JUnit dependency from the Maven marketplace by inserting the dependency in the pom.xml file that you got on our Maven project.

Add this script inside the dependencies tag in the pom.xml file.

<!-- https://mvnrepository.com/artifact/junit/junit -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.2</version>
<scope>test</scope>
</dependency>

Step 3: Create a new class file 

Now create a new class file where you will write our Junit test. To do so, follow the following steps to create a new class file.

a. Right-click on the folder src/test/java

b. Hover over to new

c. Click on the class and create a file by entering a name of your choice

Step 4: Writing the Test Script 
Now the final part is to write the JUnit test after setting up the project. Open the previously created test class file inside the src/test/java folder.

import org.junit. Test;
import org.junit. Ignore;
import static org.junit.Assert.assertEquals;

public class BrowserStackJunit {
String message = "BrowserStack is the intended message";
@Test 
public void testMessage() {
System.out. println("Inside testMessage()");
assertEquals(message, "BrowserStack is the intended message");
}

Step 5: Executing JUnit test 

Once the test is written, right-click and then select run as JUnit test.

Once the test is executed, on successful completion of the test it will be indicated on the left panel highlighted with green color.

Upon making any slight change in the test script that fails our test, it will be indicated with red color and the log of error will be displayed on the console.

Best Practices for writing JUnit Test Cases

With this Java unit testing example, you would have gained confidence in how to write JUnit test cases. However, to be more efficient in our testing, let’s look at some best practices for unit testing you can follow to ensure that your product is tested more reliably.

1. Test on Real Devices

In order to ensure a consistent and seamless user experience across all devices, always test your products on real devices before rolling them out to consumers. With all the devices readily available, setting up a digital lab becomes very difficult. Therefore, it is recommended to test on real device clouds such as using BrowserStack to keep real user conditions into account.

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2. Keep in mind the business

While writing tests for the product you must keep in mind the test aligns with the business requirements of the project.

3. Using Annotations wisely

Annotations are very useful in writing JUnit tests, as they make our code more structured and organized. Annotations were not there in JUnit 3 and are available in JUnit 4 only, which entirely revamped the JUnit testing experience.

4. Test Core methods

It is fairly difficult to write unit tests for all the components present in the project. Therefore, it is important that you write JUnit tests only for the components that are prone to bugs. Moreover, write tests for the components that are used in many parts of the project to ensure greater reliability of the project.

5. Mocking

In JUnit testing, you can only test small chunks of code. There are chances that some codes are dependent on external services, for which, you have to use third-party frameworks such as Mockito, EasyMock, and JMock for mocking external services.

Conclusion

JUnit is an open-source unit-testing framework in the world of Java development. JUnit is generally used to write automated tests. The objective of unit tests is to be done in conjunction with the development of the software, so you can run them early in the development process in order to reduce errors at the same time.

JUnit is a simple framework and does not have a steep learning curve. This comprehensive guide covered what is Unit testing, JUnit tests, how to write JUnit test cases, executed a simple test to demonstrate how JUnit functions and also discussed some practices to write efficient tests for our product. One of the most efficient yet important practices that most businesses might miss out on will be testing on a wide range of real devices. BrowserStack is a cloud-testing platform for testing applications quickly on a wide range of real devices.