A test program creates a variety of types of quality of service messages to allow a user to test the response of one or more network devices to the variety of messages. The test program displays a representation of a quality of service message on a user interface. The representation may be implemented as a tree having a branch for each section of the quality of service message. Each branch may be expanded to reveal one or more values of one or more parameters stored in the represented section. By entering a value on the user interface, the user can change the value of a parameter in represented message. The test program also allows a user to intentionally create an invalid quality of service message, such as by inserting an invalid value into one or more fields, deleting one or more required values, adding one or more invalid sections, or by deleting one or more required sections. The test program also automatically creates one or more invalid sections at the request of the user.