Combat Evolved Anniversary
The monitor of Installation 03, Testament is introduced in the second terminal in Halo: Combat Evolved Anniversary, which is narrated by his fellow monitor 343 Guilty Spark.
In the terminal Spark recalls a time shortly before the Halo Array was to be fired, when the shared knowledge network, containing much of their history, known as "the Domain" was lost to the Forerunner. Lamenting that no one may ever know anything of the Forerunner other than their weapons he recalls that Abject Testament had remarked that they deserved to be forgotten; with Spark admitting that he very well could be right.
Glasslands and Future Role in Series
Taking place after the events of Halo 3 the novel Halo: Glasslands reveals that Humanity has discovered Installation 03 and has built the research station "Ivanoff" in its orbit; though neither exploration of the Installation nor communication with Abject Testament (provided he still exists) has yet to occur.
Frank O'Connor has said that the Forerunner and post-war novels as well as the terminals in Anniversary will have connections to Halo 4, which begins a new trilogy of games. Since Abject Testament appeared in an Anniversary terminal and his Installation appears in Glasslands it is possible he could have a forthcoming role to play; if not in Halo 4 then, perhaps, another installment in the "Reclaimer" trilogy.
Like Guilty Spark and Penitent Tangent his monitor number is one of the many references to the number 7 in the Halo series. In this case it is 7 to the second power, whereas Spark and Tangent's are raised to the third and fourth powers respectively.