What is the test for determining whether a person is an aider and abettor?

In reviewing the sufficiency of the evidence on appeal, the appellate court "must review the whole record in the light most favorable to the judgment below to determine whether it discloses substantial evidence--that is, evidence which is reasonable, credible, and of solid value--such that a reasonable trier of fact could find the defendant guilty beyond a reasonable doubt." (People v. Johnson (1980) 26 Cal.3d 557, 578, 162 Cal.Rptr. 431, 606 P.2d 738.)

An aider and abettor is one who acts "with knowledge of the 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, 199 Cal.Rptr. 60, 674 P.2d 1318.) Neither mere presence at the scene of a crime, nor the failure to take steps to prevent a crime, is alone sufficient to establish that a person is an aider and abettor. Such evidence may, however, be considered together with other evidence in determining that a person is an aider and abettor. (Pinell v. Superior Court (1965) 232 Cal.App.2d 284, 287, 42 Cal.Rptr. 676.)