What is the test for admitting evidence of improper sexual activity in a sexual assault case?

In Guay v. R., 1978 CanLII 148 (SCC), [1979] 1 S.C.R. 18, 6 C.R. (3d) 130, 42 C.C.C. (2d) 536, 89 D.L.R. (3d) 532, 23 N.R. 451 [Que.], Pigeon J., delivering the judgment of the court, said (at p. 32): On the admissibility of similar fact evidence, I think it should be said that it is essentially in the discretion of the trial judge. In exercising this discretion, he must have regard to the general principles established by the cases. There is no closed list of the sort of cases where such evidence is admissible. It is, however, well established that it may be admitted to rebut a defence of legitimate association for honest purposes, as well as to rebut evidence of good character. Where the evidence is admissible on the first mentioned basis, it may be admitted as part of the case for the prosecution.