What is the test for a party to advance their case in a single action?

As Cameron J. A. noted in Zehya v. Attorney General of Canada [2004] S.J. No. 721 at para. 7: The irony of this is that the more specific and concrete their personal interest in the constitutional issues they wish to litigate thus becomes, the more difficult it becomes for them to maintain their position in the current action. Why? Because increasingly the action then amounts to a collateral attack on the judgements and orders affecting them. And it then engages the specific interests of others who are not party to the action, namely the beneficiaries of the judgments and orders. Not only that, their position then engages the principle weighing against piecemeal litigation. Parties to proceedings are expected to advance the whole of their case when the occasion arises.