The Testament of Yaru Korsin, a recording placed inside a holocron, was given by Grand Lord Yaru Korsin just before his passing in 4975 BBY. This Testament was played every twenty-five years on Testament Day until the year 3000 BBY. Within the Testament, he named his daughter Nida Korsin as his heir, detailed the organizational makeup of the Lost Tribe of Sith, approved of the execution of the spouses of Grand Lords who had died, and commanded that his alienated wife, Seelah Korsin, be exiled. This recording overwrote a previous one where Sith Lord Naga Sadow instructed Yaru to move his brother Devore Korsin along with his mining team to Phaegon III.
The original Testament recording was lost in 3000 BBY when Iliana Merko, the leader of the Sisters of Seelah, obliterated the holocron in which it was contained. However, Varner Hilts, the Caretaker, had committed the text to memory. Furthermore, copies of Korsin's Testament were preserved within the libraries located in the towns of Orreg and Elvarnos. Subsequently, during the Hilts Restoration in 2975 BBY, it was supplanted by the Testament of Varner Hilts to become the primary guiding document and legal framework for the Lost Tribe.
The Testament commenced with a declaration from Yaru Korsin stating that the Lost Tribe's ancestors were few when they initially arrived on Kesh. Because their continued existence was uncertain, the Tribe was established to ensure their survival. After gaining control of Kesh, the Tribe's founder cautioned that the only danger to the Tribe would come from within. Grand Lord Korsin also communicated to his daughter and successor, Nida Korsin, that the "true power" resided behind the throne, and that the Tribe should remember this in the face of disaster. Korsin also detailed the Tribe's hierarchy and how its structure should be managed to prevent rebellions, such as the one that ultimately resulted in his death. Additionally, the Tribe's founder advocated for the killing of the spouses of deceased Grand Lords and the banishment of his estranged wife, Seelah Korsin, who had orchestrated an attempted coup d'état intending to depose Korsin and install her own son, Jariad Korsin, as Grand Lord.
Yaru Korsin also advised those listening to promote individuals from their own group to the positions of Sith Lords and High Lords within the Circle of Lords, which served as the Tribe's governing council. This was followed by several minutes of uninteresting logistical information, which went into great detail about the Tribe's structure. Finally, Korsin ended with a statement addressed to his daughter Nida, telling her that she was the only "good thing" to come from Seelah. He also placed her in charge of the Tribe's future on Kesh. Although the Tribe did not choose to live on Kesh, Korsin contended that they could choose not to die there. That choice had to be made by his descendants. Shortly after, Korsin died, and the transmission ended.