What is the test for requesting a requested instruction on a defense?

"A trial court is required to give a requested instruction on a defense only if substantial evidence supports the defense." (People v. Panah (2005) 35 Cal.4th 395, 484.) Where substantial evidence is lacking, "the court does not err in refusing to give instructions based on that defense." (People v. Mayberry (1975) 15 Cal.3d 143, 151.) On appeal, we "ask only whether the requested instruction was supported by substantial evidence." (People v. Mentch (2008) 45 Cal.4th 274, 288.)

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