What is the test for estoppel in employment law?

Under the first question as to whether the same question has been decided, Binnie J. stated at para. 54 of Danyluk v. Ainsworth Technologies Inc, supra: … Issue estoppel simply means that once a material fact such as a valid employment contract is found to exist (or not to exist) by a court of tribunal or competent jurisdiction, whether on the basis of evidence or admissions, the same issue cannot be relitigated in subsequent proceedings between the same parties. The estoppel, in other words, extends to the issues of fact, law, and mixed fact and law that are necessarily bound up with the determination of that “issue” in the prior proceeding.