Could test scenarios be written even before code development

I have a questing about testing philosophy. In case of lacking actual test unit and description of operation within the the unit, but otherwise, provided with sufficient information on expected output, could we starting writing test case, start with elaborating on possible test scenarios or output scenarios ?

Could testers in anyway possible start any part of test case design process even before availability of test unit, or complete design but having only expected output ? The expected outputs under expected scenarios are available because of detail description from standards.