test-ob-R.el: New function to test for :result output

* test-ob-R.el (ob-session-R-result-output): This test will check if
output is printed to buffer in a session with :results output. This
test is to prevent the bug mentioned in https://list.orgmode.org/877czca7oj.fsf@u-bordeaux.fr/
does not happen again.

testing/lisp/test-ob-R.el

@@ -246,8 +246,20 @@ log10(10)
                     (string= (concat src-block result)
                              (buffer-string)))))))
 
-
-
+; add test for :result output
+(ert-deftest ob-session-R-result-output ()
+  (let (ess-ask-for-ess-directory
+        ess-history-file
+        org-confirm-babel-evaluate
+        (org-babel-temporary-directory "/tmp")
+        (src-block "#+begin_src R :session R :results output \n  1:3\n#+end_src")
+        (result "\n\n#+RESULTS:\n: [1] 1 2 3\n" ))
+    (org-test-with-temp-text
+     src-block
+     (should (progn (org-babel-execute-src-block)
+                    (sleep-for 0 200)
+                    (string= (concat src-block result)
+                             (buffer-string)))))))
 
 (provide 'test-ob-R)