A design structure is embodied in a machine readable medium for designing, manufacturing, or testing an integrated circuit. The design structure includes an input register coupled to a data processing unit input and a test operation mode and functional operation mode. In the test mode operation, the register operates in a clocked mode such that, during the test operation mode, the register propagates data to the data processing unit in response to a clock signal. In the functional operation mode, the register operates in a data flush mode such that the register propagates data to the data processing unit in response to the data. The functional mode is enabled by a flush enable signal and the test mode is enabled by an opposite state of the flush enable signal.