If you’re working with Java, chances are you’ve heard of JUnit 5. It’s the go-to tool for writing unit tests, which help you catch bugs early and make sure your code keeps working as expected. This article walks you through setting up a Maven project with JUnit 5, writing basic and advanced tests, and using its many features to keep your code solid.

Getting Started with JUnit 5 in Maven Projects

First things first, you need to add JUnit 5 to your Maven project. This involves including the right dependencies in your pom.xml file. Once that’s done, you can start writing tests. Let’s look at an example. Suppose you have a simple class that converts a fraction to a decimal:

It takes a numerator and denominator and returns the decimal value. If the denominator is zero, it throws an error to prevent division by zero. This class is straightforward but perfect for demonstrating testing.

Writing Your First Tests

To test this class, you create a separate test class. In JUnit 5, you use the @Test annotation to mark test methods. For example, you’d write one test to check if the conversion works correctly with valid input, and another to verify it throws an error when the denominator is zero.

Here’s a quick look at what those tests might look like. The first test calls the method with 3 and 4, then checks if the result is 0.75. The second test expects an exception when dividing by zero. JUnit’s Assertions class provides static methods like assertEquals and assertThrows to make this easy.

Using Assertions to Validate Results

Assertions are the backbone of testing. They compare what your code produces with what you expect. In JUnit 5, you have many options. For example, assertEquals checks if two values are the same, and assertThrows verifies that a certain exception is thrown. These help you confirm not just correct outputs but also proper error handling.

When working with floating-point numbers, you might run into small inaccuracies. JUnit’s assertEquals lets you specify a “delta” — a small margin of error. This way, you can say that 3.142 and your result are close enough if they differ by less than 0.001, for example.

Controlling Test Behavior with Annotations and Tags

JUnit 5 offers annotations to manage test execution. You can set up methods to run before or after tests, or even specify tags to include or exclude certain tests when running your suite. This is handy when you want to focus on specific parts of your tests or skip slow ones during development.

Tags are especially useful in large projects. By marking some tests with @Tag(“slow”) or @Tag(“database”), you can run only the tests you care about at the moment, saving time and resources.

Overall, mastering JUnit 5 makes your Java development more reliable and efficient. It encourages good testing habits, helps you think through edge cases, and integrates seamlessly with build tools like Maven. Whether you’re new to testing or looking to refine your skills, JUnit 5 is an essential tool in your Java toolkit.

Inspired by

• https://www.infoworld.com/article/3993538/how-to-test-your-java-applications-with-junit-5.html

Sources

• gmpg.org
• junit.org
• cucumber.io
• junit.org
• geekcap.com