What is the test for establishing that a deed which purports to convey land absolute in fee simple was intended to be, in fact, one creating a trust?

Furthermore, 'while it is true that the courts have frequently stated that clear and convincing evidence is required to justify a court in finding that a deed which purports to convey land absolute in fee simple was intended to be, in fact, one creating a trust, such rule is primarily for the trial court's guidance and if there is substantial evidence to support its conclusion the determination is not open to review on appeal.' (Teixeira v. Domingos, 171 Cal.App.2d 196, at page 201, 339 P.2d 863, at page 866.)