The easy way I do it is to make however many copies of "test0" I want, then make a trivial throwaway macro where I move my cursor to the number I want to increment, and hit M-x rolling-increment-number-at-point. (Of course with autocomplete...)

Here's my definitions:

  (defvar *rolling-counter* 0)
  
  (defun rolling-increment-number-at-point ()
    (interactive)
    (incf *rolling-counter*)
    (skip-chars-backward "0123456789")
    (or (looking-at "[0123456789]+")
        (error "No number at point"))
    (replace-match (number-to-string (+ *rolling-counter*
                                        (string-to-number (match-string 0))))))
  
  (defun clear-rolling-history ()
    (interactive)
    (setf *rolling-counter* 0))

Ow, that hurts my brain more than usual. How would one leverage registers with text instead of incremental numbers? (I will have to RTFW later.)