Russia may resume nuclear testing to make sure all its highly advanced nuclear weaponry work, notwithstanding the Nuclear Test Ban Treaty. From Scott Ritter at sputnikglobe.com:

© AFP 2023 / ALEXANDER NEMENOV
In an appearance at the plenary session of the Valdai Discussion Club on October 5, 2023, Russian President Vladimir Putin announced that Russia had successfully tested the Burevestnik “nuclear-powered global-range cruise missile.”
This effectively brought to fruition a journey he had announced back in a speech delivered on March 1, 2018 when he unveiled a series of new Russian strategic weapons designed as a response to America’s continued nullification of arms control agreements regarding missile defense.
In his 2008 address, Putin outlined the efforts undertaken by Russia over the years to get the US to scale back missile defense programs Russia viewed as representing an existential threat to its survival. “You didn’t listen to our country then,” Putin concluded. “Listen to us now.”
Chief among Russia’s concerns was that continued US pursuit of missile defense capabilities, when coupled with an American nuclear posture that envisioned the possibility of pre-emptive nuclear war, could create the conditions in which US nuclear war planners could believe that an American first strike designed to neutralize Russia’s strategic nuclear capability, when combined with a missile defense shield the US believed could shoot down most, if not all, of any Russian missiles that might survive such an attack, might actually be viable.