test for http://emacs.stackexchange.com/questions/12342/move-point-in-another-buffer-via-with-current-buffer-goto-char?noredirect=1#comment17815_12342

gistfile1.el

(let ((buf (get-buffer-create "*scratch*"))
      (text "\n;; ===\n"))
  (when (get-buffer-window buf)
    (message "Buffer is shown in some window"))
  (with-current-buffer buf
    (message "p/pm: %s/%s" (point) (point-max))
    (if (eq (point) (point-max))
        (insert text)
      (save-excursion
        (goto-char (point-max))
        (insert text)))
    (message "p/pm: %s/%s" (point) (point-max))))