What is the test for a traffic stop under the Fourth Amendment?

the Fourth Amendment when the detaining officer can point to specific articulable facts that, considered in light of the totality of the circumstances, provide some objective manifestation that the person to be detained may be involved in criminal activity." (People v. Souza (1994) 9 Cal.4th 224, 231.)

Traffic stops are treated as investigatory detentions for which the officer must be able to articulate specific facts justifying the suspicion that a crime is being committed. (People v. Wells (2006) 38 Cal.4th 1078, 1082-1083.)

Whether a police officer's conduct is reasonable under the Fourth Amendment is examined objectively, the officer's subjective motivation is constitutionally irrelevant. (Brigham City, Utah v. Stuart (2006) 547 U.S. 398, 404.)