Except for the systemTests project, all unit tests are run in the same JVM, so each test class must ensure that any modified global state is restored after the tests are run. Otherwise, subsequent tests might fail as a result.

See JDK-8239822 for a case where this actually happened and caused intermittent test failures in our nightly test runs.

The following tests call StyleManager::setDefaultUserAgentStylesheet, but do not appear to restore the state:

test/javafx/css/CssMetaDataTest
test/javafx/css/HonorDeveloperSettingsTest
test/javafx/css/Node_cssStateTransition_Test
test/javafx/css/Node_cssStyleMap_Test
test/javafx/scene/Node_effectiveOrientation_Css_Test

These should be evaluated and cleaned up where needed.