Although a written agreement to arbitrate an existing or future dispute is generally enforceable, a petition to compel arbitration will be denied when the right has been waived by the proponent's failure to properly and timely assert it. ( Code Civ. Proc., 1281, 1281.2, subd (a).) This may happen in a variety of contexts, ranging from situations in which the proponent of arbitration has previously taken steps inconsistent with an intent to invoke arbitration, to instances in which the proponent has unreasonably delayed in undertaking the procedure. There is no single determinative test of waiver, and the question for the trial court is one of fact. The question is whether the trial court's decision is supported by substantial evidence. If it is, we must affirm. If not, we may decide the issue as a matter of law. (Davis v. Blue Cross of Northern California (1979) 25 Cal. 3d 418, 425-426 [158 Cal. Rptr. 828, 600 P.2d 1060]; Christensen v. Dewor Developments (1983) 33 Cal. 3d 778, 781-782 [191 Cal. Rptr. 8, 661 P.2d 1088].)