Although a great deal of research activities in protocol testing have focused on formal method for protocol test generation in recent years, in practice many test suites are still developed in a heuristic manner. This gives rise to a strong need for test case (suite) validation before they can be used in the conformance testing of implementations under test (IUT). In this paper, we discuss the basic idea of test validation, and present an overview of TESTVAL, a tool for test case validation based on Estelle specifications. The paper also demonstrates the validity of TESTVAL by applying it to the LAPB standard test suite. From the experiments performed we find TESTVAL a useful, practical tool for test case (suite) validation. Some redundancies in the LAPB standard test suite were uncovered.