An appliance development toolkit includes a communications driver and a test engine configured to access one or more test scripts, to construct a well formed message based on instructions in the test script, and to convey the well formed message to the appliance via a communication link. Each step of the test script is separated from adjacent steps by a transition condition. The transition condition includes a logic expression resolvable to a boolean value, and a command statement that instructs what should happen so that the test engine will execute the command statement contemporaneously with a transition. 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 so that the information enables the test engine to construct the well formed message. The test engine is further configured to observe subsequent network messages, relate those to a transition logic in the test script, and evaluate the logic for transition to the next step.