What is the test for whether a police officer is justified in believing that an individual he is investigating at close range is armed?

"When an officer is justified in believing that the individual whose suspicious behavior he is investigating at close range is armed and presently dangerous to the officer or to others, it would appear to be clearly unreasonable to deny the officer the power to take necessary measures to determine whether the person is in fact carrying a weapon and to neutralize the threat of physical harm." (Terry v. Ohio (1967) 392 U.S. 1, 24, 88 S.Ct. 1868, 1881, 20 L.Ed.2d 889.)