### Question:
Section extends Group { public Section collapse(boolean newValue) { collapsed.setValue(newValue); return this; } private  Section(Element... elements); static Section of(Element... elements); Section title(String newValue); Section collapse(boolean newValue); BooleanProperty collapsedProperty(); boolean isCollapsed(); String getTitle(); StringProperty titleProperty(); Section collapsible(boolean newValue); boolean isCollapsible(); BooleanProperty collapsibleProperty();  }### Answer:
@Test public void collapseTest() { Section s = Section.of(); final int[] changes = { 0 }; s.collapsedProperty().addListener((observable, oldValue, newValue) -> changes[0] += 1); s.collapse(true); s.collapse(false); Assert.assertEquals(2, changes[0]); Assert.assertFalse(s.isCollapsed()); }