What is the test for a police officer to justify an investigative stop or detention?

Balancing these factors, the courts have concluded that in order to justify an investigative stop or detention the circumstances known or apparent to the officer must include specific and articulable facts causing him to suspect that (1) some activity relating to crime has taken place or is occurring or about to occur, and (2) the person he intends to stop or detain is involved in that activity. Not only must he subjectively entertain such a suspicion, but it must be objectively reasonable for him to do so: the facts must be such as would cause any reasonable police officer in a like position, drawing when appropriate on his training and experience (People v. Superior Court (Kiefer) supra, 3 Cal.3d at (807) p. 827, 91 Cal.Rptr. 729, 478 P.2d 449), to suspect the same criminal activity and the same involvement by the person in question. The corollary to this rule, of course, is that an investigative stop or detention predicated on mere curiosity, rumor, or hunch is unlawful, even though the officer may be acting in complete good faith. (Terry v. Ohio, supra, 392 U.S. at (1) p. 22, 88 S.Ct. 1868 (20 L.Ed.2d at 889, pp. 906-907).)