What is the test for an amended pleading?

coin: If new facts are being alleged, prejudice may easily result because of the inability of the other party to investigate the validity of the factual allegations while engaged in trial or to call rebuttal witnesses. If the same set of facts supports merely a different theory . . . no prejudice can result.' [Citation.] 'The basic rule applicable to amendments to conform to proof is that the amended pleading must be based upon the same general set of facts as those upon which the cause of action or defense as originally pleaded was grounded.' " (Garcia v. Roberts (2009) 173 Cal.App.4th 900, 910.)