What is the test to determine whether a tortfeasor can be sued for contribution?

I find the principle enunciated both at the trial level and the appellate level in Tucker v. Asleson operates to confer validity on the fourth party notice because there has not been a trial on the merits. At the trial level of Tucker v. Asleson, Finch J. adopted as correct the following statement of principle from two Ontario decisions: It is only after a trial on the merits where a person alleged to be a tortfeasor has been found not liable that such person cannot be sued for contribution by another tortfeasor. DECISION

I therefore conclude that s. 4 of the Negligence Act of British Columbia confers upon the third party, Basic Technologies, an independent right to seek contribution and indemnity from the fourth party Everest, regardless of whether Everest has entered into a settlement agreement with another party to this litigation (Prairie) by which its direct legal liability to that party has been extinguished and regardless of whether the binding effect of that settlement agreement has been confirmed in these proceedings. This conclusion is founded on the decision of our Court of Appeal in Tucker v. Asleson and the very recent decision of my brother Williamson J. in T.W.N.A. v. R. in Right of Canada. I do not find the concepts of issue estoppel or res judicata to be applicable as there has not been a determination on the merits.