A method and apparatus are disclosed that provide a technique for testing a data-processing system that enables communications between two or more telecommunications endpoints. An example of such a data-processing system is a Session-Initiation Protocol (SIP) proxy server. In particular, a test-execution system, in accordance with the illustrative embodiment of the present invention, transmits test-related signals to and receives test-related signals from one or more endpoints, such as SIP-enabled telephones. Some of the transmitted test-related signals direct an endpoint to transmit a message, such as a session-initiation request, to the data-processing system under test. Some of the received test-related signals comprise information from an endpoint, such as whether or not a message has been received from the data-processing system under test. Instead of communicating with the data-processing system itself, the test-execution system of the illustrative embodiment enlists the telecommunications endpoints to interact with the data-processing system.