What is the test for mitigation in a breach of contract case?

The principle of mitigation requires a plaintiff, whose employment has been terminated, to act reasonably and exercise diligence in seeking to replace his loss of earnings. This "duty" was described by Laskin C.J.C. in Red Deer College v. Michaels et al (1975), 1975 CanLII 15 (SCC), 57 D.L.R. (3d) 386 (S.C.C.) at 390 as follows: ... The primary rule in breach of contract cases, that a wronged plaintiff is entitled to be put in as good a position as he would have been in if there had been proper performance by the defendant, is subject to the qualification that the defendant cannot be called upon to pay for avoidable losses which would result in an increase in the quantum of damages payable to the plaintiff. The reference in the case law to a "duty" to mitigate should be understood in this sense. In short, a wronged plaintiff is entitled to recover damages for the losses he has suffered but the extent of those losses may depend on whether he has taken reasonable steps to avoid their unreasonable accumulation.