What is the test for a servant to be held accountable to his master for making a profit out of his position as a servant?

The learned trial judge then quoted the following passage of Denning, J. in Reading v. The King, [1948] 2 K.B. 268: In my judgment, it is a principle of law that if a servant, in violation of his duty of honesty and good faith, takes advantage of his service to make a profit for himself, in this sense, that the assets of which he has control, or the facilities which he enjoys, or the position which he occupies, are the real cause of his obtaining the money, as distinct from being the mere opportunity for getting it, that is to say, if they play the predominant part in his obtaining the money, then he is accountable for it to the master. It matters not that the master has not lost any profit, nor suffered any damage. Nor does it matter that the master could not have done the act himself. It is a case where the servant has unjustly enriched himself by virtue of his service without his master's sanction. It is money which the servant ought not to be allowed to keep, and the law says it shall be taken from him and given to his master, because he got it solely by reason of the position which he occupied as a servant of his master.