What is the test for granting leave and license to sublet an apartment without the landlord's consent?

The defendants rely on, among others, Carmichael v. Dolmage (1946), [1947] 1 D.L.R. 781 (B.C.C.A.). The issue in that case was whether a tenant breached the conditions of her lease by allowing her brother to move in and use her apartment. Her lease contained a clause that if she assigned or sublet her apartment without consent of the landlord, the lease would be subject to forfeiture. In order to avoid forfeiture, she had to remain the actual tenant and maintain her rights. On the advice of her solicitor, she drafted a letter to give her brother “leave and license to move in and occupy the premises ... understanding that you do not, under this arrangement, or otherwise, acquire any rights in any way derogatory to or conflicting with, or endangering my position as a tenant”. She could terminate the license without notice.