What is the test for asserting a right of silence under the Fifth Amendment?

^3. "If a person is accused of having committed a crime, under circumstances which fairly afford him an opportunity to hear, understand, and to reply, and which do not lend themselves to an inference that he was relying on the right of silence guaranteed by the Fifth Amendment to the United States Constitution, and he fails to speak, or he makes an evasive or equivocal reply, both the accusatory statement and the fact of silence or equivocation may be offered as an implied or adoptive admission of guilt." (People v. Preston (1973) 9 Cal.3d 308, 313-314.)