The word from "an industry source" is that flight tests of the Sarmat missile will begin "in the beginning of 2019." This follows a series of ejection tests that took place in Plesetsk in December 2017, March 2018, and May 2018 (although the source quoted by TASS says there were only two tests).
UPDATE: The ministry of defense insists that it carried out only two Sarmat tests - in December 2017 and in March 2018.
The book
Comments
Has Russia ever publicly declared the number of Sarmat missiles it intends to acquire?
Frank Shuler
USA
Back in 2014 they said the plan is to have 46 missiles http://russianforces.org/blog/2014/12/sarmat_deployment_plans.shtml