diff --git a/testing/lisp/test-org.el b/testing/lisp/test-org.el
index 78cd29576..b6e42dc99 100644
--- a/testing/lisp/test-org.el
+++ b/testing/lisp/test-org.el
@@ -8236,6 +8236,72 @@ two
      (call-interactively #'org-paste-subtree)
      (buffer-string)))))
 
+(ert-deftest org-test/org--open-file-format-spec ()
+  "Test `org-open-file' helper `org--open-file-format-spec'."
+  (let ((def-spec '(("s" . "file.pdf") ("1" . "10") ("2" . "pattern"))))
+    (should (equal "zathura --page 10 --find pattern file.pdf"
+		   (org--open-file-format-spec
+		    "zathura --page %1 --find %2 %s" def-spec)))
+    (should (equal "no subst"
+		   (org--open-file-format-spec
+		    "no subst" def-spec)))
+    (should (equal "simple file.pdf"
+		   (org--open-file-format-spec
+		    "simple %s" def-spec)))
+    (should (equal "with --page 10 file.pdf"
+		   (org--open-file-format-spec
+		      "with --page %1 %s" def-spec)))
+    (should (equal "file.pdf at start"
+		     (org--open-file-format-spec
+		      "%s at start" def-spec)))
+    (should (equal "in the file.pdf middle"
+		     (org--open-file-format-spec
+		      "in the %s middle" def-spec)))
+    (should (equal "literal %"
+		   (org--open-file-format-spec
+		    "literal %%" def-spec)))
+    (should (equal "literal %s in the middle"
+		   (org--open-file-format-spec
+		    "literal %%s in the middle" def-spec)))
+    (should (equal "% literal at start"
+		     (org--open-file-format-spec
+		      "%% literal at start" def-spec)))
+    (should (equal "" (org--open-file-format-spec "" def-spec)))
+    (should (equal "adjucent 10file.pdf substitutions"
+		   (org--open-file-format-spec
+		    "adjucent %1%s substitutions" def-spec))))
+
+  (should (equal "many -f first -s second -t third -e eigth file.pdf"
+		 (org--open-file-format-spec
+		  "many -f %1 -s %2 -t %3 -e %8 %s"
+		  '(("1" . "first") ("2" . "second") ("3" . "third")
+		    ("4" . "fourth") ("5" . "firth") ("6" . "sixth")
+		    ("7" . "seventh") ("8" . "eigth") ("s" . "file.pdf")))))
+
+  ;; I am afraid to add recursive substitutions like ("%s" . "recursive %s").
+  (should (equal "no-recursion-with file-%1.pdf --page 10"
+		 (org--open-file-format-spec
+		  "no-recursion-with %s --page %1"
+		  '(("s" . "file-%1.pdf") ("1" . "10")))))
+  (should (equal "no-recursion-with --search printf-%s file.pdf"
+		 (org--open-file-format-spec
+		  "no-recursion-with --search %1 %s"
+		  '(("s" . "file.pdf") ("1" . "printf-%s")))))
+
+  (let* ((err
+	  (should-error (org--open-file-format-spec "invalid-end %" ())
+			:type 'error))
+	 (text (cadr err)))
+    (should (and (stringp text)
+		 (string-match-p "’invalid-end <ERROR ->%’" text))))
+  (let* ((err
+	  (should-error (org--open-file-format-spec "missed --subst %1 %s"
+						    '(("s" . "file.pdf")))
+		       :type 'error))
+	 (text (cadr err)))
+    (should (and (stringp text)
+		 (string-match-p "’missed --subst <ERROR ->%1 %s’" text)))))
+
 (provide 'test-org)
 
 ;;; test-org.el ends here