Erik Šabič sent a pull request (patches 741b864 and 209971b) against 2f91e79,
which is not a release.
This is a diff between 0.19 and those 2 patches applied against 0.19.

So, when 0.20 will be released, this patch can be removed.

The procedure should be as simple as reverting the commit including
this file then calling `guix refresh emacs-helpful`.
diff --git a/test/helpful-unit-test.el b/test/helpful-unit-test.el
index a07aa8e..8a95129 100644
--- a/test/helpful-unit-test.el
+++ b/test/helpful-unit-test.el
@@ -119,7 +119,9 @@ bar")))
   (should
    (equal
     (helpful--docstring #'test-foo-advised t)
-    "Docstring here too.")))
+    (if (version< emacs-version "28")
+        "Docstring here too."
+    "Docstring here too.\n\nThis function has :around advice: `ad-Advice-test-foo-advised'."))))
 
 (defun test-foo-no-docstring ()
   nil)