What is the test for determining whether a plaintiff's cause of action is in furtherance of their right to petition or free speech?

City of Cotati v. Cashman (2002) 29 Cal.4th 69, 78, 124 Cal.Rptr.2d 519, 52 P.3d 695, original italics.) An "act underlying the plaintiff's cause of action must itself have been an act in furtherance of the right of petition or free speech." (Ibid . original italics.) Courts must look to "the act underlying the cause of action, not the gist of the cause of action." (Wallace v. McCubbin (2011) 196 Cal.App.4th 1169, 1190, 128 Cal.Rptr.3d 205.)