What is the test for a murder committed by a "willful, deliberate and premeditated killing"?

Murder committed by a "willful, deliberate, and premeditated killing" is murder in the first-degree. ( 189.) To sustain a conviction for first-degree murder, the prosecution must prove more than that the defendant intended to kill his victim. (People v. Cole (2004) 33 Cal.4th 1158, 1224 (Cole).) "Deliberation" is the careful weighing of considerations when forming a course of action, and "premeditation" means the defendant thought over his course of action in advance. (Ibid.) The process of premeditation and deliberation does not require any extended period of time. (Ibid.) " ' " 'The true test is not the duration of time as much as it is the extent of the reflection. Thoughts may follow each other with great rapidity and cold, calculated judgment may be arrived at quickly.' " ' [Citation.]" (Ibid.)