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

## Overview
As  previously mentioned, JUnit Jupiter and JUnit Vintage both run on the same platform. JUnit Vintage can run JUnit 4 and JUnit 3 tests. JUnit Jupiter uses a different package name, so it doesn’t conflict with the existing JUnit 4. Tests written with the new JUnit Jupiter programming model and legacy JUnit 4 tests can coexist in the same project. If we have legacy projects with JUnit 4 tests and want to leverage the new programming model in JUnit Jupiter, we have three options when upgrading to JUnit 5:
- We can keep the legacy JUnit 4 tests and runtime and use the JUnit 5 platform and Jupiter for new tests only.
- We can use JUnit Vintage to run legacy JUnit 4 tests and use JUnit Jupiter to run new tests.
- We can upgrade legacy JUnit 4 tests to use the JUnit Jupiter programming model and use JUnit Jupiter only.

We use a Spring Boot application created by **Spring Initializer** as the legacy application. We’ll see how to migrate this application using the three options above.

## JUnit 4 and 5 runtimes
The legacy Spring Boot application already has JUnit 4 configured with a simple JUnit 4 test. We can keep the configuration and tests untouched and use JUnit Jupiter to write and execute new tests. We simply need to configure JUnit 5 to the application, following the instructions in Chapter 3 (**Annotations, Tagging, and Filtering**). For Gradle, after enabling the JUnit 5 plugin, the standard task test is disabled by default. To run JUnit 4 tests, we use the configuration in the code below to enable the task test. We can then use a Gradle test to run both JUnit 4 and 5 tests.

# Overview
As  previously mentioned, JUnit Jupiter and JUnit Vintage both run on the same platform. JUnit Vintage can run JUnit 4 and JUnit 3 tests. JUnit Jupiter uses a different package name, so it doesn’t conflict with the existing JUnit 4. Tests written with the new JUnit Jupiter programming model and legacy JUnit 4 tests can coexist in the same project. If we have legacy projects with JUnit 4 tests and want to leverage the new programming model in JUnit Jupiter, we have three options when upgrading to JUnit 5:
- We can keep the legacy JUnit 4 tests and runtime and use the JUnit 5 platform and Jupiter for new tests only.
- We can use JUnit Vintage to run legacy JUnit 4 tests and use JUnit Jupiter to run new tests.
- We can upgrade legacy JUnit 4 tests to use the JUnit Jupiter programming model and use JUnit Jupiter only.

We use a Spring Boot application created by **Spring Initializer** as the legacy application. We’ll see how to migrate this application using the three options above.

# JUnit 4 and 5 runtimes
The legacy Spring Boot application already has JUnit 4 configured with a simple JUnit 4 test. We can keep the configuration and tests untouched and use JUnit Jupiter to write and execute new tests. We simply need to configure JUnit 5 to the application, following the instructions in Chapter 3 (**Annotations, Tagging, and Filtering**). For Gradle, after enabling the JUnit 5 plugin, the standard task test is disabled by default. To run JUnit 4 tests, we use the configuration in the code below to enable the task test. We can then use a Gradle test to run both JUnit 4 and 5 tests.

Understand the usage of JUnit 4 and Junit 5 runtimes.

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

JUnit 4 Migration

Overview

JUnit 4 and 5 runtimes