An intertwined test specification (ITTS) is used for controlling Automated Test Equipment (ATE) to apply a sequence of stimulus signals to a device under test (DUT) during a stimulus run and to validate returned response signals during a validation run. The ITTS has response validation scripts intertwined with stimulus invoking scripts where the response validation scripts are conditionally executed during the validation run but not during the stimulus invoking run. Response signals are logically associated with unique stimulus identification codes so that appropriate response signals can be matched with corresponding validation scripts even if the response signals are returned out-of-order to the ATE or to a response logging unit interposed between the ATE and the DUT.