Hi all,

Currently tests with missing dependency are silently skipped -- it
might be worth changing this behavior to not skip them, but mark them
as expected to fail. You can do this in ERT by placing the
keyword :expected-result followed by either :passed or :failed before
the test's body.

Benefit of this is that the tests w/ missing dependencies will show up
in the ERT result page (with a small letter f) but (obviously) don't
count as failures.

The following macro is a first shot at a convenient way to define
tests with dependencies:

#+begin_src emacs-lisp
  (defmacro org-test-deftest-with-dependency (dependency &rest body)
    (let* ((docstring (if (stringp (third body)) (list (third body))))
           (deftest (nthcdr (if docstring 3 2) body))
           (dependency-p (eval dependency)))
      `(ert-deftest ,@(append (list (first body) (second body)) docstring)
           ,@(if dependency-p
                 '(:expected-result :passed)
               '(:expected-result :failed (error "Missing dependency")))
         ,@deftest)))
#+end_src

Here DEPENDENCY is a simple form that evaluates to non-nil if the
dependency is met. If marking the tests this way is the agreed way to
go we can extend the syntax of a dependency to an alist with a
human-readable description of the dependency as key and a list of
forms that all must eval to non-nil as value. E.g.

#+begin_src emacs-lisp
  (defvar test-ob-R-dependencies
    '(("R executable" (org-test-for-executable "R"))
      ("Package ESS" (featurep 'ess))))
#+end_src

And change the expander code to map through this alist and as soon one
dependency evals to nil sets a variable `dependency-missing' to the
respective dependency.

Any comments on this?

Best,
  -- David
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