What is the test for rescinding a contract where the contract was signed in error?

Alternatively, the party seeking to rescind the contract also could obtain relief by showing the following facts: (1) the mistake was regarding his basic assumption in making the contract; (2) the mistake had a material affect on the agreed exchange of performances adverse to him; (3) the party did not bear the risk of the mistake; and (4) that it would be unconscionable to enforce the contract. (See Donovan v. RRL Corp., supra, 26 Cal.4th at p. 282.)