What is the test for adding new defendants on the motion of an existing defendant?

In Court of Milan Bankruptcy Proceedings v. Yorkton Securities Inc., 1999 BCCA 774, 132 B.C.A.C 67, the court considered an appeal from a decision overturning the refusal of a master to add new defendants on the motion of an existing defendant. In restoring the decision of the master, the court considered the words “just and convenient” as found in Rule 15(5)(a), and identified a number of factors that a court should consider in addressing them, including: a) whether the proposed amendments relate to a common subject matter with the existing action, b) the failure of the moving party to take steps earlier by way of legal action, c) the length of time the moving party has been aware of the claim, and d) the cost and delay that would occur if new parties were added.