What is the test for an aider and abettor to be liable for an attempted robbery?

"An attempted robbery requires a specific intent to commit robbery and a direct, ineffectual act (beyond mere preparation) toward its commission." (People v. Medina (2007) 41 Cal.4th 685, 694.) An aider and abettor must "act with knowledge of the

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criminal purpose of the perpetrator and with an intent or purpose either of committing, or of encouraging or facilitating commission of, the offense." (People v. Beeman (1984) 35 Cal.3d 547, 560, italics omitted.) Among the factors the jury may consider in determining aiding and abetting liability are presence at the crime scene, companionship, and conduct before and after the offense. (People v. Nguyen (2015) 61 Cal.4th 1015, 1054.)