diff --git a/actionmailer/test/mail_helper_test.rb b/actionmailer/test/mail_helper_test.rb
index a8ab19a95c0e3..e49eabdce8275 100644
--- a/actionmailer/test/mail_helper_test.rb
+++ b/actionmailer/test/mail_helper_test.rb
@@ -121,4 +121,16 @@ def test_use_cache
       assert_equal "Greetings from a cache helper block", mail.body.encoded
     end
   end
+
+  def helper
+    Object.new.extend(ActionMailer::MailHelper)
+  end
+
+  def test_block_format
+    assert_equal "  * foo\n", helper.block_format(" * foo")
+    assert_equal "  * foo\n", helper.block_format("   * foo")
+    assert_equal "  * foo\n", helper.block_format("* foo")
+    assert_equal "  * foo\n*bar", helper.block_format("* foo*bar")
+    assert_equal "  * foo\n  * bar\n", helper.block_format("* foo * bar")
+  end
 end