prevent error in Octave process, add tests, update test docs

* lisp/ob-octave.el (org-babel-execute:octave):

  -Ensure that the special Octave variable `ans' is bound when
  GFX-FILE is non-nil.  The glue code in
  ORG-BABEL-OCTAVE-WRAPPER-METHOD causes Octave to exit with a
  non-zero exit code when `ans' is not bound.

  -Change format control string to %S from %s.  Ensure the graphics
  filename is quoted.  If it is not, Octave may create a mis-named
  file or fail entirely.

* testing/examples/ob-octave-test.org:

  Update the Graphical tests section:
  -put in the correct headers;
  -add a remark about where to find each test.

* testing/lisp/test-ob-octave.el:

  Add the three tests ob-octave/graphics-file,
  ob-octave/graphics-file-session and ob-octave/graphics-file-space.

  -ob-octave/graphics-file: The first test verifies that the first bug
  identified above is fixed; it also verifies that graphics file
  creation works correctly for scripting.

  -ob-octave/graphics-file-session: The second test verifies graphics
  file creation works correctly for sessions.  The Octave command
  `crash_dumps_octave_core(0)' is included to prevent the creation of
  a core file (`octave-workspace').

  -ob-octave/graphics-file-space: The third test verifies that a
  graphics filename with a space in it is created correctly.

Thanks to Ihor Radchenko for helpful feedback.
Ref: https://list.orgmode.org/8735asbtfe.fsf@localhost/T/#u

lisp/ob-octave.el

@@ -91,7 +91,7 @@ end")
 				 (list
 				  "set (0, \"defaultfigurevisible\", \"off\");"
 				  full-body
-				  (format "print -dpng %s" gfx-file))
+				  (format "print -dpng %S\nans=%S" gfx-file gfx-file))
 				 "\n")
 		    full-body)
 		  result-type matlabp)))

testing/examples/ob-octave-test.org

@@ -46,10 +46,18 @@ ans = s
 
 
 * Graphical tests
-#+begin_src octave :results graphics :file chart.png
+
+Graphics file.  This test is performed by =ob-octave/graphics-file= in =testing/lisp/test-ob-octave.el=.
+#+begin_src octave :results file graphics :file sombrero.png
 sombrero;
 #+end_src
 
-#+begin_src octave :session
+Graphics file in a session.  This test is performed by =ob-octave/graphics-file-session= in =testing/lisp/test-ob-octave.el=.
+#+begin_src octave :session :results graphics file :file sombrero.png
+sombrero;
+#+end_src
+
+Graphics file with a space in name.  This test is performed by =ob-octave/graphics-file-space= in =testing/lisp/test-ob-octave.el=.
+#+begin_src octave :results graphics file :file sombrero hat.png
 sombrero;
 #+end_src

testing/lisp/test-ob-octave.el

@@ -64,4 +64,69 @@
     (org-babel-next-src-block 5)
     (should (equal nil (org-babel-execute-src-block)))))
 
+(ert-deftest ob-octave/graphics-file ()
+  "Graphics file.  Test that link is correctly inserted and graphics file is created (and not empty).  Clean-up side-effects."
+  ;; In case a prior test left the Error Output buffer hanging around.
+  (when (get-buffer "*Org-Babel Error Output*")
+    (kill-buffer "*Org-Babel Error Output*"))
+  (let ((file (make-temp-file "test-ob-octave-" nil ".png")))
+    (unwind-protect
+        (org-test-with-temp-text
+	    (format "#+begin_src octave :results file graphics :file %s
+sombrero;
+#+end_src"
+		    file)
+          (org-babel-execute-src-block)
+          (should (search-forward (format "[[file:%s]]" file) nil nil))
+          (should (file-readable-p file))
+          (should (> (file-attribute-size (file-attributes file)) 0))
+          (should-not (get-buffer "*Org-Babel Error Output*")))
+      ;; clean-up
+      (delete-file file)
+      (when (get-buffer "*Org-Babel Error Output*")
+        (kill-buffer "*Org-Babel Error Output*")))))
+
+(ert-deftest ob-octave/graphics-file-session ()
+  "Graphics file in a session.  Test that session is started in *Inferior Octave* buffer, link is correctly inserted and graphics file is created (and not empty).  Clean-up side-effects."
+  (let ((file (make-temp-file "test-ob-octave-" nil ".png")))
+    (unwind-protect
+        (org-test-with-temp-text
+	    (format "#+begin_src octave :session :results file graphics :file %s
+crash_dumps_octave_core(0);
+sombrero;
+#+end_src"
+		    file)
+          (org-babel-execute-src-block)
+          (should (get-buffer "*Inferior Octave*"))
+          (should (search-forward (format "[[file:%s]]" file) nil nil))
+          (should (file-readable-p file))
+          (should (> (file-attribute-size (file-attributes file)) 0))
+          (should-not (get-buffer "*Org-Babel Error Output*")))
+      ;; clean-up
+      (delete-file file)
+      (let (kill-buffer-query-functions kill-buffer-hook)
+        (kill-buffer "*Inferior Octave*"))
+      (when (get-buffer "*Org-Babel Error Output*")
+        (kill-buffer "*Org-Babel Error Output*")))))
+
+(ert-deftest ob-octave/graphics-file-space ()
+  "Graphics file with a space in filename.  Test that session is started in *Inferior Octave* buffer, link is correctly inserted and graphics file is created (and not empty).  Clean-up side-effects."
+  (let ((file (make-temp-file "test ob octave-" nil ".png")))
+    (unwind-protect
+        (org-test-with-temp-text
+	    (format "#+begin_src octave :results file graphics :file %s
+sombrero;
+#+end_src"
+		    file)
+          (org-babel-execute-src-block)
+          (should (search-forward (format "[[file:%s]]" file) nil nil))
+          (should (file-readable-p file))
+          (should (> (file-attribute-size (file-attributes file)) 0))
+          (should-not (get-buffer "*Org-Babel Error Output*")))
+      ;; clean-up
+      (delete-file file)
+      (when (get-buffer "*Org-Babel Error Output*")
+        (kill-buffer "*Org-Babel Error Output*")))))
+
+
 (provide 'test-ob-octave)