JDK-8218469, fix was made to correct the rendering of JSlider as the Slider knob/head was not being rendered at all. The reason was that gtk3 changed the way styles are used. No automated test was written to verify the results. Current bug is to write the automated tests for the same.
JDK-8221781 was created to add automated tests for a number of fixes done related to gtk3. The current fix covers JSlider widget from the widgets listed in JDK-8221781