@Override
	void addTransactionListener(DomainObjectAdapterDB object, TransactionListener listener) {
		if (object != domainObj) {
			throw new IllegalArgumentException("invalid domain object");
		}
		transactionListeners.add(listener);
	}
Returns the undo stack depth (The number of items on the undo stack).

<p>
This method is for JUnits.

@return the undo stack depth
Ghidra/Framework/Project/src/main/java/ghidra/framework/data/DomainObjectTransactionManager.java