(1) A test that checks attachment or controller circuitry (without checking the connected device) by returning the output of the attachment of controller circuitry as input. For example, when irrecoverable communications adapter or machine errors occur, the wrap test can transmit a specific character pattern to or through the modem in a loop and then compare the character pattern received to what was transmitted.
(2) For devices, a diagnostic test that returns the output of a device as input.