What is the test for police to have reasonable suspicion in making arrests?

In reviewing the district court's ruling on the motion to suppress, we will uphold findings of fact--what information the officers had, what acts were performed, and what statements were made--unless they are clearly erroneous. United States v. Uribe-Velasco, 930 F.2d 1029, 1032 (2d Cir.1991). We review de novo the district court's determination of whether the police had reasonable suspicion. United States v. Springer, 946 F.2d 1012, 1015 (2d Cir.1991).

A police officer may in appropriate circumstances and in an appropriate manner stop a person for purposes of investigating possibly criminal behavior even though there is no probable cause to make an arrest. Terry v. Ohio, 392 U.S. 1, 22, 88 S.Ct. 1868, 1880, 20 L.Ed.2d 889 (1968). The test is whether