### Question:
DragAndDropHelper { void setTop(final HTMLElement element, final int top) { element.style.setProperty(TOP, top + PX); } DragAndDropHelper(final HTMLElement dragArea,
                             final HTMLElement addButtonContainer);   }### Answer:
@Test public void testSetTop() { final HTMLElement element = mock(HTMLElement.class); final CSSStyleDeclaration style = mock(CSSStyleDeclaration.class); final int expected = 123; element.style = style; helper.setTop(element, expected); verify(style).setProperty(TOP, expected + PX); }