During the design of an embedded system, fixing errors discovered only in later stages is a very expensive activity. In order to decrease such costs, the engineers have to identify and fix the introduced errors as soon as possible. Therefore, it makes sense to facilitate the errors detection during the whole the design cycle, including the initial specification stages. This work proposed a test-based approach to aid the early verification of embedded and real-time systems. The proposed approach applies test cases on the system behavior described in the high-level specifications. A tool to automate the execution of the test cases upon UML models has been created. Its initial goal is to improve the errors detection on the system behavior before the implementation phase, since test cases are based on the system requirements. Test cases are platform independent and describe: runtime scenarios; the behaviors to be tested along with their input; and the expected results. The tool executes automatically each test case, in which the specified behavior is simulated Thereafter, the obtained results are compared with the expected ones, indicating the success or failure of the test case. A case study was performed to validate the proposed approach. The achieved results demonstrate that it is feasible to test the system behavior even though when the implementation is still not available.