What is the test for "rule of lenity" in a criminal statute?

Second, "[a]s a criminal statute, section 848 'must be strictly construed, and any ambiguity must be resolved in favor of lenity.' " United States v. Long, 654 F.2d 911, 914 (3d Cir.1981) (quoting United States v. Emmons, 410 U.S. 396, 411, 93 S.Ct. 1007, 1015, 35 L.Ed.2d 379 (1973)). See also Bifulco v. United States, 447 U.S. 381, 387, 100 S.Ct. 2247, 2252, 65 L.Ed.2d 605 (1980) (rule of lenity applies to penalties imposed by criminal statutes as well as substantive scope of criminal prohibitions).