What is the test for brief detentions?

... detentions must be brief. They attract an obligation for the police to explain the reason for the detention and, in light of R v. Suberu, supra, an obligation to advise the detainee of his or her s. 10(b) Charter right to retain and instruct counsel. They involve no search authority beyond a reasonable safety pat-down. And, finally, they impose no obligation on detainees to respond to police questioning. Thus, while such detentions represent an intrusion on personal liberty, that intrusion is limited. ...