Waiting for predicate to be true

[canatella]

Would you accept a pull request with a function that takes a predicates and wait with a timeout for the predicate to be true ? I have a mode which is launching async commands to fill a buffer. In my test I need to wait for the buffer to be filled. I was thinking something along the lines of:

(defmacro ert-wait-for (timeout predicate &rest body)
  "Wait for maximum TIMEOUT second for PREDICATE to verify, than execute forms in BODY."
  `(with-timeout
       (,timeout (ert-fail (format "Timeout of %ds exceeded while waiting for predicate." ,timeout)))
     (while (not (funcall ,predicate))
       (accept-process-output nil 0.05))
     ,@body))

So one could use it like

(ert-deftest test-buffer-content ()
  (with-current-buffer my-buffer
    (ert-wait-for 10 (lambda ()
                       (goto-char (point-min))
                       (= (how-many "foobar" 2)))
      (goto-char (point-min))
      (should (re-search-forward "the foobar is in the foobar" nil t)))))

to wait for a buffer to contain twice foobar for example. I think this might be usefull for other users of async commands.

[rejeep]

Is the buffer contents inserted async?

Anyways, I don't think this is the appropriate library for such a function as it's not async, which is the purpose of this library?

[canatella]

Yes the buffer content is the output of an async function started with start-process. But maybe I misunderstood this library purpose. If I understood correctly, with your lib, I could use a callback in my process sentinel and use ert-deftest-async to assert that the callback has been called before timeout. I found that, for me, going the way of the wait-for function was easier as it allows to also verify the side effect of the callback (like switching to a buffer or creating a new one). Anyway if you have a better suggestion, for my problem or for another library where this could be usefull, it's welcome.