* @param prev
* @param next
* @param expectedOperationCount
*/
protected void assertDiff(VirtualElement prev, VirtualElement next, int expectedOperationCount) {
Node prevNode = prev.dom != null ? prev.dom : prev.materialize();
Node nextNode = next.dom != null ? next.dom : next.materialize();
clean(next);
List<Patch> ops = PatchDiff.diff(prev, next);