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 `assertNull()` method
The `assertNull()` method asserts that the given `Object` is `null`.
- If the actual value is `null`, the test case passes.
- If the actual value is `not null`, the test case fails.



It has three different overloaded methods:

public static void assertNull(Object actual)

public static void assertNull(Object actual, String message)

public static void assertNull(Object actual, Supplier<String> messageSupplier)


- The `assertNull(Object actual)` method is the simplest form that only accepts a single `Object` to check.
- For the `assertNull(Object actual, String message)` method, when the `Object` isn’t `null`, it fails with the given message.
- The `assertNull(Object actual, Supplier<String> messageSupplier)` method uses the `messageSupplier` to retrieve the failure message lazily.

# Examples of `assertNull()` 

Let’s look at some examples for the methods above.

- The usage of `assertNull(Object actual)` can be seen in **lines 7–12** in the function `testAssertNullWithNullString()`. The test passes because the `Object` passed is `null`.
- Another overloaded function of `assertNull()` is `assertNull(Object actual, String message)` in the function `testAssertNullWithMessage()`, in **lines 14–20**. The test doesn’t pass because `null` isn’t an empty string being passed.
- The last overloaded function is `assertNull(Object actual, Supplier messageSupplier)`, used in the function `testAssertNullWithMessageSupplier()`, in **lines 22–28**. Once again, the test doesn’t pass.

Learn about assertNull() and assertNotNull() 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: assertNull() and assertNotNull()

The `assertNull()` method

Library Management System

Assertions: assertNull() and assertNotNull()

The assertNull() method

The `assertNull()` method