This paper describes a test method which relies on the actual observation of supply current (IDD) waveforms. The method can be used to supplement the standard IDDQ test method and it can be easily applied to dynamic and low VDD, low Vt CMOS circuits. The method allows us to detect faults which may not be detected by IDDQ test methods, and is sensitive enough to detect potential faults, which do not manifest themselves as functional errors. A simple built-in current sensor, which proves to be adequate in verifying the feasibility of using the IDD waveforms analysis is proposed to safely observe the current waveforms without significantly changing the waveforms.