What is the test for an intervenor in a civil matter?

3] … [I]t is clear that where the applicant does not have a 'direct' interest in the litigation, the court must consider the nature of the issue before the court (particularly whether it is a 'public' law issue); whether the case has a dimension that legitimately engages the interests of the would-be intervenor; the representativeness of the applicant of a particular point of view or 'perspective' that may be of assistance to the court; and whether that viewpoint will assist the court in the resolution of the issues or whether, as noted in Ward v. Clark, the proposed intervenor is likely to 'take the litigation away from those directly affected by it.' ...