As a best practice, unit test classes that are run by Junit should not extend javafx.application.Application. JUnit constructs an instance of a test class for each test method that it runs. This will be different from the instance of the object that is constructed when Application.launch method is called, and this can lead to unexpected behavior. See the code review for JDK-8193445 for a case where this caused a problem.

Most of our tests use helper classes or nested (static) classes as subclasses of Application, but the following two test classes do not:

tests/system/src/test/java/test/com/sun/javafx/image/impl/ImageRaceTest.java
tests/system/src/test/java/test/javafx/scene/control/AccordionTitlePaneLeakTest.java

This isn't causing any problems today, but we should consider fixing them to follow best practices.