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

The principles relating to the assessment of damages arising out of a breach of a contract were fully discussed by Laskin C.J.C. in Red Deer College v. Michaels (1975), 1975 CanLII 15 (SCC), 57 D.L.R. (3d) 386 (S.C.C.). The headnote thereto summarized the governing principles 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. In that sense the plaintiff is under a “duty” to mitigate. . . . If it is the defendant’s position that the plaintiff could reasonably have avoided some part of the loss claimed, it is for the defendant to carry the burden of that issue, subject to the defendant being content to allow the matter to be disposed on the trial Judge’s assessment of the plaintiff’s evidence on avoidable consequence.