Abstract: A test harness is provided for fully testing an enterprise application integration (“EAI”) environment. The test harness is preferably used with a GUI-based test tool and includes a test controller, a message collector and a test validator. The test controller transmits control signals to the message collector to configure the message collector to “listen” for predefined messages on a message bus. If a message matches the configuration rules, the test validator compares the message to a set of validation rules. If the message matches the validation rules, the test is deemed a success. Test-created messages may also be injected onto the bus by a message generator and unavailable EAI applications may be simulated by a test responder. Preferably, the message collection and generation configurations are based on templates created from previously stored messages. Off-bus applications may be tested by employing a message “tee” coupled to the bus.