An appliance development toolkit includes an editor configured to create one or more test scripts having steps with each step being separated from its adjacent steps by a transition condition. The transition condition includes a logic expression resolvable to a boolean transition value, and one or more command statements that instruct what should happen so that a test engine can execute the command statement contemporaneous with the transition from one step to another. The toolkit also includes information associated with a message element in a message data payload. The message data payload is uniquely identifiable within a universe of pre-defined message data payloads for an appliance. The toolkit also includes a converter for placing the test script into a form for use in diagnosing an appliance.