What is the test for the principle of reasonableness in the context of costs?

Borins J.A. explained the rationale for the principle in Moon v. Sher: The failure to refer, in assessing costs, to the overriding principle of reasonableness, can produce a result that is contrary to the fundamental objective of access to justice. The costs system is incorporated into the Rules of Civil Procedure, which exist to facilitate access to justice. There are obviously cases where the prospect of an award of costs against the losing party will operate as a reality check for the litigant and assist in discouraging frivolous or unnecessary litigation. However, in my view, the chilling effect of a costs award of the magnitude of the award in this case generally exceeds any fair and reasonable expectation of the parties. In deciding what is fair and reasonable, as suggested above, the expectation of the parties concerning the quantum of a costs award is a relevant factor.[5]