@Override
	void doUndo(boolean notify) throws IOException {
		if (canUndo()) {
			SynchronizedTransaction t = undoList.removeLast();
			redoList.addLast(t);
			t.undo();
			if (notify) {
				notifyUndoableListeners();
			}
		}
	}
Returns the undo stack depth.
(The number of items on the undo stack)
This method is for JUnits.
@return the undo stack depth
Ghidra/Framework/Project/src/main/java/ghidra/framework/data/SynchronizedTransactionManager.java