A test system that includes a generator and an analyzer acting cooperatively to test a device having a plurality of device communication channels. The device has a plurality of inputs and corresponding outputs, each input being connected to a corresponding one of the outputs. The correspondence between the input and output channels may change if the device is turned off and on or if the device is not actively sending data from the inputs to the outputs. The test system determines a mapping between the device inputs and outputs prior to performing bit error rate testing utilizing a mapping test pattern. The test system can then switch to a bit error rate test pattern without causing the device to drift such that the correspondence between the input and output channels is lost.