What is the test for determining whether a settlement is enforceable?

"It is for the trial court to determine in the first instance whether the parties have entered into an enforceable settlement. [Citation.] In making that determination, 'the trial court acts as the trier of fact, determining whether the parties entered into a valid and binding settlement. [Citation.] Trial judges may consider oral testimony or may determine the motion upon declarations alone. [Citation.] When the same judge hears the settlement and the motion to enter judgment on the settlement, he or she may consult his [or her] memory. [Citation.]' [Citation.]" (Osumi v. Sutton (2007) 151 Cal.App.4th 1355, 1360.)