“Waterfield Test” — This test helps to determine the limits of police authority to interfere justifiably with a person’s liberty or property — for instance, during random stops and detentions.
Also called the common law “ancillary power doctrine,” the Waterfield Test is set down in R. v. Waterfield,  3 All E.R. 659,  1 Q.B. 164 (C.C.A.). It is referenced in R. v. Stenning, 1970 CanLII 12 (SCC),  3 C.C.C. 145, 10 D.L.R. (3d) 224,  S.C.R. 631.
The court found that: ” … it is probably more convenient to consider what the police constable was actually doing and in particular whether such conduct was prima facie an unlawful interference with a person’s liberty or property. If so, it is then relevant to consider whether (a) such conduct falls within the general scope of any duty imposed by statute or recognized at common law and (b) whether such conduct, albeit within the general scope of such a duty, involved an unjustifiable use of powers associated with the duty.”
R. v. Kelsy, 2011 ONCA 605 (CanLII)
R. v. Simpson, 1993 CanLII 3379 (ON CA)