An apparatus, method, and computer program product are disclosed for identifying types of errors that occur in a communications device under test and where only the presence of an error is indicated by an error checker. Each presence of an error bit in an error signal during a first period of time output from the error data checker is identified. The error bit indicates only that a mismatch occurred between an input signal input into the device and an output signal output from the device. The error bit is generated in response to an error in the device under test. The error bit includes no information about a type of the error. The type of the error is determined by determining a number of occurrences of the error bit in the error signal during the first period of time.