I want to use my org-mode documentation as a sort of quasi-unittest; I want to execute the whole buffer, and be notified if marked cells' new results differ from their previous results. E.g,

#+begin_src python :results verbatim :exports both :wrap example :notify_on_change


Suppose x3 is changed and now x3(10) returns 40. I want to be notified that this change has happened (and get a diff of the two results).

PS: If this should be possible for visual (image) results, it would be really awesome.

PPS: Is there any testing framework that works like this? I.e., it only reports change, and does not need you to manually hardcode values?

  • 1
    AFAIK, there is nothing built-in to Org mode that would alow you to do that: you'll have to build it yourself. My inclination would be to use source control as @mankoff suggests, rather than try to use babel directly, although you can use a babel SRC block to run the unit tests and do the comparisons, based on the saved "gold" files that contain the previous output.
    – NickD
    Mar 15, 2021 at 12:22

1 Answer 1


One idea might be to save a copy of the current buffer, run the tests, and then run a diff command on them.

(defun run-tests ()
  (copy-to-buffer "*my-test*" (point-min) (point-max))
  (diff-buffers "*my-test*" (current-buffer)))

This will make a new buffer showing the diff (if any). There are lots of variations I suppose, like writing to files, different ways of diffing.

It would be hard I think to get this to work for images.

[edit]: here is a version that works on a copy of the buffer with ediff.

(defun run-tests ()
  (let ((contents (buffer-string))
    (buf (current-buffer)))
    (with-current-buffer (get-buffer-create "*my-test*")
      (insert contents)
      (ediff-buffers buf "*my-test*"))))
  • I use magit for this.
    – mankoff
    Mar 15, 2021 at 11:38
  • Magic is a clever idea for files in a git repo. That also makes it easy to revert them back to the state you want them. Mar 15, 2021 at 12:35
  • @mankoff Can you add your workflow as an answer?
    – HappyFace
    Mar 15, 2021 at 12:57
  • @JohnKitchin I find ediff-buffers better than diff-buffers. This solution works pretty great. How can I execute the temp buffer instead of the main one?
    – HappyFace
    Mar 15, 2021 at 13:12
  • 1
    @HappyFace I added an example that I think works on a copy and uses ediff. Mar 15, 2021 at 14:01

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