What is the test for estimating damages for breach of contract?

In doing so I am mindful of the principle expressed in Wood v. Grand Valley Railway (1915), 51 S.C.R. per Davies J at p. 289: “It was clearly impossible under the facts of that case [Chaplin v. Hicks] to estimate with anything approaching to mathematical accuracy the damages sustained by the plaintiffs, but it seems to me to be clearly laid down there by the learned judges that such an impossibility cannot “relieve the wrongdoer of the necessity of paying damages for this breach of contract” and that on the other hand the tribunal to estimate them whether jury or judge, must under such circumstances do “the best it can” and its conclusion will not be set aside even if the amount of the verdict is a matter of guess work.”