A method and system for testing voice applications, such as VoiceXML applications, is provided. The system provides a run-time simulation environment for voice applications that simulates and automates user interaction. A user simulation script is provided in a customized mark-up language. The voice application is processed to derive a nominal output of the voice application. The user simulation script is processed to generate a simulated output for the voice application corresponding to the nominal output. The user simulation script is also processed to generate a simulated input for the voice application corresponding to a pre-determined user input to the voice application. The simulated inputs and outputs are executed in conjunction with the voice application in real-time to test the application. Execution time rates for text based input and output are calculated based on empirical speaking rates of human users.