diff --git a/guides/source/action_mailbox_basics.md b/guides/source/action_mailbox_basics.md
index 5daf79fdc1..708654d7e3 100644
--- a/guides/source/action_mailbox_basics.md
+++ b/guides/source/action_mailbox_basics.md
@@ -373,3 +373,5 @@ class ForwardsMailboxTest < ActionMailbox::TestCase
   end
 end
 ```
+
+Please refer to the [ActionMailbox::TestHelper API](https://api.rubyonrails.org/classes/ActionMailbox/TestHelper.html) for further test helper methods.