What is the legal test for a refugee seeking to enter Canada on good grounds of persecution?

In Adjei v. Canada (Minister of Employment and Immigration) 1989 CanLII 5184 (FCA), [1989] 2 F.C. 680, MacGuigan J.A. commented on the required level of risk of future persecution, at para. 8: What is evidently indicated by phrases such as "good grounds" or "reasonable chance" is, on the one hand, that there need not be more than a 50% chance (i.e., a probability), and on the other hand that there must be more than a minimal possibility. We believe this can also be expressed as a "reasonable" or even a "serious possibility", as opposed to a mere possibility. [emphasis added]