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 `fail()` method
The `fail()` method fails a test with a given message and/or `Throwable`. Below are the overloaded
methods of `fail()`.

fail(String message)
fail(Supplier<String> messageSupplier)
fail(Throwable cause)
fail(String message, Throwable cause)


A `fail()` actually has a generic return type so that a single `fail()` statement can be used as a
lambda expression.
# Examples of `fail()`
Let’s look at some examples of the method above:
- **Lines 4–8:** The `simpleFail()` function fails a test.
- **Lines 10–18:** The `simpleFailWithSupplierMessage()` function fails a test with a supplier message.
- **Lines 20–24:** The `testMethodWithThrowable()` function fails a test with a throwable.
- **Lines 26–30:** The `testMethodWithThrowableAndMessage()` function fails a test with a throwable and a message.


Let's describe the fail() and assertInstanceOf() methods 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

Assertions: fail() and assertInstanceOf()

The `fail()` method

Library Management System

Assertions: fail() and assertInstanceOf()

The fail() method

The `fail()` method