What is the test for failure to mitigate in circumstances where a plaintiff has not pursued recommended medical treatment?

The test for failure to mitigate in circumstances where a plaintiff has not pursued recommended medical treatment is summarized in Chiu v. Chiu, 2002 BCCA 618 at para. 57:

The onus is on the defendant to prove that the plaintiff could have avoided all or a portion of his loss. In a personal injury case in which the plaintiff has not pursued a course of medical treatment recommended to him by doctors, the defendant must prove two things: (1) that the plaintiff acted unreasonably in eschewing the recommended treatment, and (2) the extent, if any, to which the plaintiff’s damages would have been reduced had he acted reasonably. These principles are found in Janiak v. Ippolito, 1985 CanLII 62 (SCC), [1985] 1 S.C.R. 146.