A testing probe functioned as a specific type of instrument. The droid informant 8t88 experienced the loss of an arm on the moon Nar Shaddaa in the year 5 ABY, and subsequently journeyed to the moon Sulon for Galactic Empire-related dealings, where he tried to fix himself. As 8t88 was in the process of affixing a replacement arm, he requested his bodyguard Rol to provide him with a tuning stylus; however, Rol, unable to distinguish between the two, mistakenly provided a testing probe. In a fit of anger, 8t88 threw away the testing probe and proceeded to utilize the tuning stylus for the installation of his new arm.
The somewhat vague testing probe made its initial appearance in the 1998 novella Dark Forces: Rebel Agent, authored by William C. Dietz. While its precise function wasn't stated, its name suggests it was intended for testing purposes. This tool also makes a brief appearance in the audio drama adaption of Rebel Agent. Nevertheless, the tool is not directly named in the audio drama.