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

## Extension interface
After test instances are created by JUnit, we can post-process them using extensions. This is useful when we want to inject custom dependencies into test instances or invoke custom logic on test instances. The extension interface for test instances post-process is `TestInstancePostProcessor`. It only has one method, `void postProcessTestInstance(Object testInstance, ExtensionContext context) throws Exception`. The `testInstance` parameter is the test instance to process. The `ExtensionContext` is also passed to retrieve context information. 

Suppose that some test cases require configuration information contained in the class `Config`. We can have a `ConfigAware` interface to set the `Config` object. See the code below, for example.

# Extension interface
After test instances are created by JUnit, we can post-process them using extensions. This is useful when we want to inject custom dependencies into test instances or invoke custom logic on test instances. The extension interface for test instances post-process is `TestInstancePostProcessor`. It only has one method, `void postProcessTestInstance(Object testInstance, ExtensionContext context) throws Exception`. The `testInstance` parameter is the test instance to process. The `ExtensionContext` is also passed to retrieve context information. 

Suppose that some test cases require configuration information contained in the class `Config`. We can have a `ConfigAware` interface to set the `Config` object. See the code below, for example.

Understand how to test instances post-process using TestInstancePostProcessor 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

Test Instance Post-processing

Extension interface