All of our programs are open source. If you have the PyPose program -- you already have the source. Python is just a scripting langauge, open PyPose.py or any of the .py files in a text editor and you'll see. (alternatively, you can browse the source on arbotix.googlecode.com, click on Source tab).
The TEST command is basically our in-house way of checking out an ArbotiX before shipping it. To trigger it, send out:
0xff 0xff 253 2 25 231
The protocol is the same as talking to an AX-12 itself (basically, the PyPose sketch acts as a bus pass through, or, given special instructions, it executes commands). The first two 0xff are the header for the packets (just like an AX-12 would recieve). The 253 is the ID, your servos are IDs 1-X, 253 tells the arbotiX this packet SHOULD NOT be passed through, and that it instead should interpret the packet itself. 25 is the instruction (arbotiX test or ARB_TEST). The 2 is the length of the packet (see the AX-12 datasheet or the PyPose.py source for details, but general format = # of parameters + 2, test takes no parameters). The 231 is a checksum (255 - ((id + length +instruction + any parameters)%256)). All of the other special arbotiX commands, such as loading a sequence, loading the poses that are part of a sequence, or playing it, follow this format.