What is the test for determining whether a person is entitled to "free leave" when confronted by a police officer?

"The test is necessarily imprecise, because it is designed to assess the coercive effect of police conduct, taken as a whole, rather than to focus on particular details of that conduct in isolation. Moreover, what constitutes a restraint on liberty prompting a person to conclude that he is not free to 'leave' will vary, not only with the particular police conduct at issue, but also with the setting in which the conduct occurs." (Michigan v. Chesternut (1988) 486 U.S. 567, 573.)