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

In Red Deer College v. Michaels (1975), 1975 CanLII 15 (SCC), 57 D.L.R. (3d) 386 at p. 390 (S.C.C.), Laskin J. stated the basic principle on the issue of mitigation of damages as follows: . . . The primary role in breach of contract cases, the 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 upon whether he has taken reasonable steps to avoid their unreasonable accumulation . . .