Can a single witness be substantial evidence in a civil case?

The testimony of a single witness can be substantial evidence so long as the testimony is credible and of solid value. (Casella v. SouthWest Dealer Services, Inc. (2007) 157 Cal.App.4th 1127, 1143-1144.) West Bay does not claim that its own witnesses are not credible, and there is no other evidence in the record that conflicts with their testimony. West Bay does not contend it was not paid for Cleveland's work on or before November 5, 2007; it argues only that the selected date of November 5 is "speculation."