What is the test for appeal against a cost award?

It is important to state that the awarding and fixing of costs is highly discretionary and is afforded significant deference, and leave to appeal a costs order is granted sparingly. For example, in House v. Baer, 2017 ONCA 885 at paras. 86–87, the court observed that leave to appeal costs will only be granted in obvious cases where the party seeking leave convinces the court there are “strong grounds upon with the appellant court could find that the judge erred in exercising his discretion” and that “a court should set aside a costs award on appeal only if the trial judge has made an error in principle or if the cost awarded is plainly wrong” (citations omitted).