What is the test for mitigation in a motor vehicle accident?

The law is clear on the issue of mitigation: while the plaintiff has the burden of proving both the fact that she has suffered damage, and the quantum of that damage, the burden of proof moves to the defendant if he alleges the plaintiff could have and should have mitigated her loss. The plaintiff is required to act reasonably, and cannot expect to be compensated for damages sustained by reason of her own negligence or unreasonable behaviour. Janiak v. Ippolito 1985 CanLII 62 (SCC), [1985] 1 S.C.R. 146, at para. 32 and 33.