What is the legal test for a judge pro tempore?

5 The court rejected the argument that the constitutionally required 'stipulation' must be an agreement between at least two parties: 'It must be remembered that the 'stipulation' required is that 'of' and not 'between' the litigants. The decision to refer a pending cause to a judge pro tempore, and the selection of the individual member of the bar who is to so act, are, in the end, with the court, which must approve and order the designation, not with the litigant. If 'agreement' is here required, it is the agreement between court and litigant which controls.' (Barfield v. Superior Court, supra, 216 Cal.App.2d at p. 479, 31 Cal.Rptr. at p. 32.)