Add missing unit-test for getDigitalRoot
Add missing unit-test for getDigitalRoot

Arnold77777/js-assignments,scurimich/js-assignments,Spoyke/rolling-scopes-js-assignments,FedorovD/js-assignments,IgorOzimuk/js-assignments,PROteinBY/js-assignments,urahara-dono/js-assignments,aorgish/rolling-scopes-js-assignments,mishka3097/js-assignments,rolling-scopes-school/js-assignments,andrei6184/js-assignments