What is the test for contempt of an injunction against a party who is not a party to the action?

"[I]t has been a common practice to make the injunction run also to classes of person through whom the enjoined party may act, such as agents, servants, employees, aiders, abetters, etc., though not parties to the action, and this practice has always been upheld by the courts, and any of such parties violating its terms with notice thereof are held guilty of contempt for disobedience of the judgment. But the whole effect of this is simply to make the injunction effectual against all through whom the enjoined party may act, and to prevent the prohibited action by persons acting in concert with or in support of the claim of the enjoined party, who are in fact his aiders and abetters. As we have said, this practice is thoroughly settled and approved by the courts, and there is a fair foundation for a conclusion that persons so co-operating with the enjoined party are guilty of a disobedience of the injunction." (Berger v. Superior Court of Sacramento County, supra, 175 Cal. at p. 721. Italics in original.)