Structured testing criteria are usually used to assess the adequacy of test case sets, defining coverage measures. Control and data flow based criteria employ information about the program graph as well as definition and usage of variables to establish the testing requirements. In this paper, we present an approach to prototype supporting tools for control and data flow based criteria. In the proposed approach, we use TXL — a language based in the transformational paradigm — to analyze and instrument the program under test. The instrumentation aims at making it possible to process the data by a Prolog program which allows the tester to assess the test case set adequacy. A simple example is used to illustrate the main ideas of our approach.