Gain insights into JUnit 5, explore its advantages over JUnit 4, and delve into its features like assertions, parameterized tests, dependency injection, and test execution order. Discover hands-on projects to cement your skills.

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JUnit 5 is a standard framework for unit testing in Java. Released in 2017, JUnit 5 is a major improvement over JUnit 4 and supports a lot of new methods. Many projects have migrated from JUnit 4 to JUnit 5. JUnit 5 is also the default test framework for new projects. JUnit 5 is composed of three sub-projects: JUnit Platform, JUnit Jupiter, and JUnit Vintage. Details of these sub-projects are discussed in the course.

This course first discusses the advantages of JUnit 5 over the previous versions and then jumps directly into tests. The course includes discussion on assertions, assumptions, tagging and filtering, nested tests, dependency injection, repeated tests, parameterized tests, dynamic tests, test instance lifecycle, extension model, JUnit 4 migration, JUnit platform, and test execution order. 

By the end of this course, you’ll be deeply familiar with unit testing in JUnit 5. There’s also a little project for you at the end to put your newly acquired skills to the test.

All About JUnit5

## The `UserService` class
For parameterized tests, JUnit 5 provides built-in converters for some parameter types. We can also create custom converters using the `@ConvertWith` annotation and the `org.junit.jupiter.params.converter.ArgumentConverter` interface. The `ArgumentConverter` interface has only one method, `Object convert(Object source, ParameterContext context) throws ArgumentConversionException`. The first parameter, `source`, is the input object for conversion. This method returns the converted object based on the input object.

Suppose we need to add tests for a user management application. We have a predefined list of example users for testing. We need to find a way to quickly inject user objects into the test methods so we can easily verify those user objects. We can have user IDs as the argument values and use a custom argument converter to convert them.

The `UserService` class in the below code is the service class to load `User` objects by IDs. The `User` class contains three fields, `id`, `name`, and `email`. The `UserService` class uses an in-memory map to store the users.

# The `UserService` class
For parameterized tests, JUnit 5 provides built-in converters for some parameter types. We can also create custom converters using the `@ConvertWith` annotation and the `org.junit.jupiter.params.converter.ArgumentConverter` interface. The `ArgumentConverter` interface has only one method, `Object convert(Object source, ParameterContext context) throws ArgumentConversionException`. The first parameter, `source`, is the input object for conversion. This method returns the converted object based on the input object.

Suppose we need to add tests for a user management application. We have a predefined list of example users for testing. We need to find a way to quickly inject user objects into the test methods so we can easily verify those user objects. We can have user IDs as the argument values and use a custom argument converter to convert them.

The `UserService` class in the below code is the service class to load `User` objects by IDs. The `User` class contains three fields, `id`, `name`, and `email`. The `UserService` class uses an in-memory map to store the users.

Understand how to use the argument converter in JUnit 5.

Getting Started

Writing Basic Tests

Annotations, Tagging, and Filtering

Nested tests in JUnit 5

Dependency Injections

Parameterized and Dynamic Tests

Test Instance Lifecycle in JUnit 5

Extension Model

JUnit Platform

Test Execution Order

Conclusion

Library Management System

Argument Converter

The `UserService` class

Library Management System

Argument Converter

The UserService class

The `UserService` class