private <W extends Widget & HasAllDragAndDropHandlers> void verifyDragEnterEventSink(W w) {
DragEnterHandlerImpl handler = new DragEnterHandlerImpl();
w.addDragEnterHandler(handler);
assertFalse(handler.hasEventFired());
w.fireEvent(new DragEnterEvent() {
});
assertTrue(handler.hasEventFired());
}