Writing Java Code: A Practical Guide to JUnit5

Java is a popular programming language for computer programming of all kinds. Millions of programmers use Java because it is simple and can be executed on the majority of computers. Java code developers develop using the assistance of JUnit Testing.

Testing is verifying if your code works correctly. Without testing, bugs can end up with users and create issues. JUnit simplifies testing by helping testers to write little programs, referred to as tests, that verify their code.

In this article, we will learn JUnit5. We will also learn how to install it, write the first test, and take advantage of its best features. By the end of it, you will be in a position to make your Java code safer and highly trustworthy.

What is JUnit5?

JUnit5 is the latest and simplest Java code test tool. It is compatible with Java 8 and updated versions, so you can use all the new Java features. There are three parts of JUnit5: JUnit Platform that runs tests, JUnit Jupiter for the new tests, and JUnit Vintage for old tests.

With JUnit5, tests are written without any difficulties in straightforward annotations such as @Test and @BeforeEach. Tests can be grouped, executed with varying data, or skipped if necessary. JUnit5 is quicker, more adaptable, and the ideal testing software for new Java projects.

Installing JUnit5 in Your Java Project

It is easy to start using JUnit5 and code more efficiently and securely in Java. The following are the steps you need to take to include JUnit5 in your project:

1. Install Java

You must ensure that Java has been installed on your device. JUnit5 supports Java 8 or updated versions. 

2. Select and Install an ID

Do select any feasible Integrated Development Environment (IDE) such as IntelliJ IDEA, Eclipse, or Visual Studio Code. These make writing, executing, and upkeep of tests quite simple.

3. Create a New Java Project

To create a new Java project, you can use your preferred IDE, Maven, or Gradle, and also work and manage your project’s libraries and dependencies.

4. Add JUnit5 to Your Project

JUnit5 can be included as a dependency in projects working with Maven or Gradle. It guides the project on how to download and use it. Your IDE or build tool can easily handle the downloading and setup for you.

5. Set Up the Test Directory

Make a separate directory for your test files within your project. It is typically named test or src/test/java. Put all your test files here so that all your stuff is organized.

6. Make a Simple Test

Create a new test file in your testing directory. Create a very basic test, for example, a test that 2 + 2 = 4. This is how you test if all is well.

7. Run the Test

Test with your build tool or IDE. If a green tick or a message that the test passed appears, you can rest assured that your configuration is fine.

8. Begin Writing Additional Tests

You can now start writing more tests on your Java code. Keep your tests in the test directory and utilize JUnit5 features as you learn about them.

Basic Unit Testing Principle

Unit testing is a procedure of great importance, it verifies that small portions of code, a method, or a class are operating as required. This is fairly done by setup, execution, and verification of the result. 

Writing Your First JUnit5 Test

It is simple to implement your initial test with JUnit5, and it is one way of ensuring your code does exactly what you are expecting it to do.

1. Define the Class to Test

To begin testing a Java class, declare the class you wish to test (Calculator, for example) and then use the multiply function. That means the code that you want to ensure works as desired.

2. Declare a Test Class

Create a test class later on. The test class that is named CalculatorTest is typically the same as the main class, but includes the Test at the end, organizing tests for you.

3. Add Test Methods with Annotations

In your test class, you create methods to check whether your code is correct. You use special words known as annotations. The @Test method is important as it shows the method as a test, calls the desired method, and asserts the correctness of the result.

4. Utilize Assertions

Assertions are tests that verify what you expect and what you get. For instance, you can verify whether 4*5 equals 20. If you get it right, the test is successful. If not, the test is a failure and will also inform you what went wrong.

5. Install Before Each Test

You can use @BeforeEach to execute some code prior to executing each test. This proves useful if you would like to have something prepared, such as a fresh calculator object, each time.

6. Run Your Test

Run your test in your build or in your IDE. If your test passes, you see a green bar or check. If your test fails, you see a red bar and a message indicating what failed. This is easier for you to debug.

Important JUnit5 Annotations and How They Are Utilized

JUnit5 uses certain annotations to determine how your tests execute and behave.

• @Test: Marks a method to be a test. The code inside this method will run using JUnit5.
• @BeforeEach: Runs code as a pretest. Use a pretest to initialize the items you need for testing.
• @AfterEach: Executes code following a test. Utilize this to clean up and reset after a test.
• @BeforeAll: Runs code once before all tests in a class. Suitable for things you don’t want to repeat, such as opening a database.
• @AfterAll: Runs code once after completion of all tests. Use it to release resources or perform an end-of-test clean-up.
• @DisplayName: Provides you with a means to provide a friendly name for your test. This makes your test reports more readable.
• @RepeatedTest: This annotation helps to perform a test more than once.
• @Disabled: If you don’t want to run a test, this annotation suppresses it.

With the help of these JUnit5 annotations, you can improve the readability and usability of your tests.

Assertions in JUnit5

Assertions are the building blocks of any test. Assertions are crucial in testing code performance, helping in infinite context testing, and ensuring safety and reliability. They ease out for the failure of tests and provide information on any issues, thereby enhancing the overall quality of your programs.

Testers and developers usually use assertions to make sure the code is coming up with the correct values in their tests.

• assertEquals: It helps to assert the equality of two values.
• assertTrue: This verifies the truth of a statement in the code.
• assertFalse: Checks that something is false.
• assertNotNull: Checks if something is not null.
• assertThrows: Checks that a method will throw an exception.

Organizing and Structuring Tests

Name your tests so that you can quickly find and fix bugs. Use names with a description, such as CalculatorTest for test classes and shouldMultiplyNumbers for test methods. Also, place all the test classes in one folder. It is easy to run the tests, and your project will look clean later.

Let’s take an example, you can put your tests in one folder in this format: test or src/test/java, and group similar tests.

Parameterized Tests

At times, you wish to test your code with various data. JUnit5 helps you with ease through parameterized tests via the @ParameterizedTest annotation. You can test one test using various values, which is effective. You can test various cases as well. It helps your code work with various inputs, not solely one.

Advanced JUnit5 Features

JUnit5 does have some specific characteristics through which you can develop smart and dynamic tests.

• Conditional Test Run: Use @EnabledIf and @DisabledIf to execute or skip tests depending on conditions such as Operating System (OS) or environment. This enables tests to be executed only when necessary.

• Test Tagging and Filtering: Use the tag “fast,” “slow,” or others with @Tag. This allows you to choose easily which tests to execute in large projects.

• Custom Display Names: The @DisplayName annotation provides tests with human-readable, comprehensible names such that test reports are easier to understand and read.

• Dynamic Tests: Dynamically create tests at runtime to test numerous similar cases without duplicating similar test statements.

• Better Test Management: These capabilities provide control and management of large sets of tests so that testing becomes more efficient and flexible as your project grows.

Cloud Integration for JUnit5

Cloud integration makes it possible to run your JUnit5 tests on other devices in the cloud, and it makes it possible to test quicker, easier, and more accurately on many different devices.

LambdaTest is an AI testing tool that is fully compatible with JUnit 5 and can complement modern approaches such as ChatGPT test automation, where AI-driven assistants help generate and optimize test cases alongside traditional frameworks. It enables real-time testing on 3,000+ browsers, devices, and OS combinations, including real Android and iOS devices. With built-in support for Selenium WebDriver and other popular frameworks, LambdaTest provides a scalable and reliable infrastructure for end-to-end test automation.

LambdaTest and JUnit5 make it simple to run tests in parallel on several devices. This reduces the time of running the tests and facilitates the detection of bugs. This is particularly useful when running code tests on various environments such as browsers and OSs.

LambdaTest supports integration with Continuous Integration/ Continuous Deployment (CI/CD) pipelines, such that tests automatically run in the cloud when code is changed. LambdaTest further supports using Selenium WebDriver for testing web applications on various environments.

It is easy to integrate JUnit5 with LambdaTest. You simply need to add some configuration and use the LambdaTest plugin or SDK. Once you have logged in and connected, your tests will execute on the LambdaTest cloud with instantaneous feedback and comprehensive reports.

By choosing LambdaTest for cloud testing, you ensure your application runs everywhere. It is an excellent option for teams who want to take advantage of what Selenium WebDriver with JUnit5 offers and require stable, scalable, and simple test automation in the cloud.

Mocking and Dependency Injection in Tests

At times, your code relies on some other entity, i.e., a web service or a database. Rather than the actual thing, mockings allow you to implement mock versions of these dependencies so that tests can be run more efficiently and reliably. Tools like Mockito operate in conjunction with JUnit testing to provide you with the ease of creating and using these mocks.

For instance, dependency injection enables testing and modification of code through the supply of a mock from the external environment and the prevention of live database usage in tests.

Best Practices for Writing Good Tests

The following are the best practices for writing a good test;

• Independent Tests: Independent tests must be independent and must never have any dependency on other tests.

• Use Simple Names: You could use simple and expressive names to make your tests simpler and easier to access.

• Make Tests Repeatable: Irrespective of the number of times you execute a test, it should give the same result every time.

• Properly Set Up and Clean Up: You should always pre-set the data required by a test before running it to avoid tests from interfering with each other. You can also clean it up after running the test.

• Write Readable Tests: Also, ensure that your tests are readable and understandable so anyone can read and understand them easily.

Common Pitfalls and Solutions of JUnit5

The following are the common pitfalls and their solutions:

• Overuse/Underuse of Mocks: Reduce the number of fake objects you use, but don’t sacrifice the crucial tests in the process.

• Ignoring Failed Tests: Never disregard failed tests; always return to them.

• No Updates with code change: Keep the tests updated to make sure that they continue to validate the right parts while looking through code changes.

• Writing Ambiguous and Dependent Tests: Also, avoid writing tests that completely rely on other tests to work.

Conclusion 

To sum up, making your software secure and stable is possible with Java with JUnit5 coding. You can detect and correct bugs early with experience in coding and executing tests. Practice more and learn new features so you can test your code even better.