On this page:
contract-random-generate

7.11 Random generation

procedure

(contract-random-generate ctc fuel [fail])  any/c

  ctc : contract?
  fuel : int?
  fail : (-> any/c) = (λ () (error ...))
Attempts to randomly generate a value which will match the contract. The fuel argument limits how hard the generator tries to generate a value matching the contract and is a rough limit of the size of the resulting value.

The generator may fail to generate a contract, either because some contracts do not have corresponding generators (for example, not all predicates have generators) or because there is not enough fuel. In either case, the thunk fail is invoked.