What is the test for determining the mens rea of sexual assault?

For example, as Major, J. stated for the Majority in R v. Ewanchuk 1999 CanLII 711 (SCC), [1999] 1 SCR 330, a case in which an accused engaged the 17 year old female complainant, in a series of progressively more intimate sexual advances: Speaking of the mens rea of sexual assault in Park, supra, at para. 39, L'Heureux‑Dubé J. (in her concurring reasons) stated that: . . . the mens rea of sexual assault is not only satisfied when it is shown that the accused knew that the complainant was essentially saying "no", but is also satisfied when it is shown that the accused knew that the complainant was essentially not saying "yes". Para. 45 [My emphasis added].