It appears as if the sets are being modified in-place (rather than copied), which means that they are equal, when they shouldn't be. I have @Ignore'd this test for now. The test fails on the indicated line:

@Test public void ensureImpl_getPseudoClassStateReturnsValidValue() {
        Set<PseudoClass> value1 = comboBox.getPseudoClassStates();
        assertFalse(comboBox.isEditable());
        assertTrue(value1.size() >= 0);
        
        comboBox.setEditable(true);
        Set<PseudoClass> value2 = comboBox.getPseudoClassStates();
        assertTrue(value2.contains(PseudoClass.getPseudoClass("editable")));
        
        comboBox.show();
        Set<PseudoClass> value3 = comboBox.getPseudoClassStates();
        assertTrue(value3.contains(PseudoClass.getPseudoClass("showing")));
        
        comboBox.arm();
        Set<PseudoClass> value4 = comboBox.getPseudoClassStates();
        assertTrue(value4.contains(PseudoClass.getPseudoClass("armed")));
        
        assertFalse(value1.equals(value2)); // TEST FAILS HERE
        assertFalse(value1.equals(value3));
        assertFalse(value1.equals(value4));
        assertFalse(value2.equals(value3));
        assertFalse(value2.equals(value4));
        assertFalse(value3.equals(value4));
    }