The official Twitter account for Kadokawa's BookWalker service confirmed on March 31 that Tetsuto Uesu and illustrator Nekosuke Ōkuma's The Testament of Sister New Devil (Shinmai Maō no Testament) light novel series has ended with the 13th volume. The 13th volume shipped on March 31.
The first 12-episode season of the television anime adaptation of the light novel series premiered in January 2015. Crunchyroll streamed the first season in various territories as it aired. The second season, titled The Testament of Sister New Devil BURST, premiered in October 2015. Crunchyroll also streamed the second season as it aired in Japan. The anime received an original anime disc with the seventh volume of the manga. A separate OVA, titled The Testament of Sister New Devil Departures, screened in Japan in 2018 and then released on home video in March 2018. Crunchyroll began streaming that OVA in August 2019.
Miyakokasiwa launched a manga adaption of Uesu's novels in Kadokawa's Monthly Shōnen Ace magazine in May 2013, and the manga has nine total volumes. Seven Seas Entertainment released the manga in North America, as well as the five-volume spin-off manga The Testament of Sister New Devil Storm! by Fumihiro Kiso.
Source: BookWalker's Twitter account