What is the test for a vehicle stop?

The particular Vehicle and Traffic Law section which the officer relies on to justify the stop must also be closely examined because on occasion, the courts have found that the officer made a mistake of law and ruled the stop invalid. Where the officer's belief is based on an erroneous interpretation of law, the stop is illegal at the outset and any further actions by the police as a direct result of the stop are illegal. Byer v. Jackson 241 AD2d 943 (Fourth Dept. 1997).