In the context of safety-critical systems, which are real-time reactive systems, testing process must be integrated with the software development process as a whole, not just with the end product. Consequently, measuring the efficiency of the testing process emerges as an important issue. To be accurate and meaningful, both the measurement and the components to be measured must be precisely described. The measurement should conform to the axioms of measurement theory, and the software development process should be grounded on rigorous formalism. In this paper we introduce test adequacy measurement for measuring the efficiency of testing process integrated into a rigorous environment for developing real-time reactive systems. The test data adequacy measurement associates a degree of test set adequacy according to the test data adequacy criterion to indicate how adequately the testing has been performed. There are two important measures associated with every test data adequacy criterion and minimum number of test cases. The measurement method is illustrated with Train-Gate-Controller design, a bench-mark example in real-time system design.