diff --git a/README.org b/README.org
index c04863b..e208d4a 100644
--- a/README.org
+++ b/README.org
@@ -3743,6 +3743,7 @@ facilities for [[https://orgmode.org/worg/org-tests/index.html][Testing Org]].
 #+name: lst:setup-org-mode-test-2
 #+begin_src emacs-lisp -n
 (with-eval-after-load 'emacs
+  ;; Stolen from `org-test-run-all-tests'.
   (defun org-test-run-some-tests ()
     "Run some defined tests.
 Load all test files first."
@@ -3771,9 +3772,19 @@ Load all test files first."
     (org-test-load)
     (let (;; Catch errors in diary sexps better.
           (calendar-debug-sexp t))
-      (ert "ob/"))))
-#+end_src
+      (ert "ob/")))
 
+  (defun org-test-run-a-test-file ()
+    "Run all tests in an Org test file (trailing `/' matters).
+Examples: `ob/' or `ob-maxima'."
+    (interactive)
+    (let ((text (read-string "Org test file (without leading test-): "
+                             nil nil "ob-maxima")))
+      (org-test-load)
+      (let (;; Catch errors in diary sexps better.
+            (calendar-debug-sexp t))
+        (ert text))))))
+#+end_src
 
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