end - to - end testing of applications across networks is enabled . to test the application and the infrastructure subsystems , an application server connected to the network contains an application under test . a response simulator is connected to the other end of the network . a test module is accessible to the application and to the simulator and contains a test message to be transmitted to the simulator , and an expected response message from the simulator . the application transmits each test message and compares a response message from the simulator to an expected response message . the simulator obtains the response to each test message from the test module .