Run devtools::test_that on file save

davtools-test.el

(defun devtools-test ()
;;Run test_that on each save by Brian Malehorn
;;http://stackoverflow.com/questions/32257685/running-rdevtooltest-that-on-buffer-save-in-ess
  (interactive)
  (when
       (let* ((old (current-buffer)))
      (string-match (rx-to-string `(: ".R" eos) t) (buffer-name))
    (switch-to-buffer "*R*")
    (end-of-buffer)
    (insert "devtools::test()")
    (comint-send-input)
   (switch-to-buffer old))))

(add-hook 'after-save-hook 'devtools-test)