We propose a new method for generating digital-clock tests for realtime systems. That is, tests which can observe time with only a finite precision. Our goal from testing is to check the conformance of a given implementation with respect to a given specification (the model). The method is based on the socalled action refinement techniques. The main benefit of the method is to save memory space needed to build and to store tests. One important contribution of this work is a simplified way for both modelling and testing real-time systems. We first write a (high-level) simplified version of the model of the system, as an input-output transition system (IOTS) and then we refine it into a more detailed (low-level) model as a timed input-output transition system (TIOTS). This same mechanism applies to the test generation procedure.