It is well known that the output signals measured by an automatic test equipment (ATE) system are not only due to the device-under-test (DUT), but also due to the test path. For example, if the intersymbol interference (ISI) due to the test path is not negligible, then the performance of the DUT can be grossly underestimated. In this paper, we propose a generic model for both the test path and the DUT. By using a cascading model, we will illustrate the measured signals due to the test path and DUT combined, in contrast to the measured signals due to the DUT alone. We will investigate both the effect of the limited bandwidth and the effect of ringing. We will illustrate the eye-diagrams of the DUT, and conceptually identify and separate the impact of the test path on the eye-diagrams.