What is the test for a defendant to plead guilty to a lesser included crime?

When the accusatory pleading describes a crime in the statutory language, as in the present case, the test for a lesser included offense is simply that, where the charged "offense cannot be committed without necessarily committing another offense, the latter is a necessarily included offense." (People v. Greer (1947) 30 Cal.2d 589, 596, 184 P.2d 512; People v. Anderson (1975) 15 Cal.3d 806, 809, 126 Cal.Rptr. 235, 543 P.2d 603.) Thus we must inquire in the present case whether robbery, the greater offense, can be committed without necessarily committing an assault. If it can, assault is not a lesser included offense in robbery.