What is the legal test for "premeditated" murder?

First degree murder is a "willful, deliberate, and premeditated killing." (Pen. Code, 189.) "In this context, `premeditated' means `considered beforehand,' and `deliberate' means `formed or arrived at or determined upon as a result of careful thought and weighing of considerations for and against the proposed course of action.' [Citations.]" (People v. Mayfield (1997) 14 Cal.4th 668, 767.) "An intentional killing is premeditated and deliberate if it occurred as the result of preexisting thought and reflection rather than unconsidered or rash impulse. [Citations.]" (People v. Stitely (2005) 35 Cal.4th 514, 543.) Premeditation and deliberation do not require "an extended period of time." (People v. Mayfield, supra, 14 Cal.4th at p. 767.) "`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 . . . .' [Citations.]" (Ibid.)

Although reviewing courts typically consider evidence of preexisting "motive, planning activity, and manner of killing" to assess the sufficiency of the evidence for premeditation and deliberation, "[t]hese factors need not be present in any particular combination . . . ." (People v. Stitely, supra, 35 Cal.4th at p. 543.) "The method of killing alone" may suffice to prove premeditation and deliberation. (People v. Memro (1995) 11 Cal.4th 786, 863-864.)