What is a "protective sweep" and what is the test for such a sweep?

"A 'protective sweep' is a quick and limited search of premises, incident to an arrest and conducted to protect the safety of police officers or others. It is narrowly confined to a cursory visual inspection of those places in which a person might be hiding." (Maryland v. Buie (1990) 494 U.S. 325, 327 (Buie).) "The sweep lasts no longer than is necessary to dispel the reasonable suspicion of danger and in any event no longer than it takes to complete the arrest and depart the premises." (Id. at pp. 335-336.)