What is the test for determining who is to be a trustee in a personal injury case?

The case at bar seems to me clearly distinguishable from what was held in MacDonald v. Norwich Union, 10 P.R. 462, in which case one “M.,” having effected certain insurances in his favour, assigned one of the policies to the plaintiff, one of his creditors, and the other to one “C.” as trustee for the benefit creditor. In actions under such policies it was held that “M.” could be examined as a person for whose immediate benefit the suits were prosecuted. In that case the assignor was clearly interested; he, or his estate, would only receive the benefit of the policies if the suit determined in favour of the plaintiff. If an adverse judgment were recovered, he could not bring a subsequent action.