diff --git a/lib/action_mailbox/test_helper.rb b/lib/action_mailbox/test_helper.rb
index 23b2bb02ca..680e8b43be 100644
--- a/lib/action_mailbox/test_helper.rb
+++ b/lib/action_mailbox/test_helper.rb
@@ -5,14 +5,15 @@ module ActionMailbox
     # Create an InboundEmail record using an eml fixture in the format of message/rfc822
     # referenced with +fixture_name+ located in +test/fixtures/files/fixture_name+.
     def create_inbound_email_from_fixture(fixture_name, status: :processing)
-      create_inbound_email file_fixture(fixture_name).read, status: status
+      create_inbound_email_from_source file_fixture(fixture_name).read, status: status
     end
 
     def create_inbound_email_from_mail(status: :processing, **mail_options)
-      create_inbound_email Mail.new(mail_options).to_s, status: status
+      create_inbound_email_from_source Mail.new(mail_options).to_s, status: status
     end
 
-    def create_inbound_email(source, status: :processing)
+    # Create an `InboundEmail` using the raw rfc822 `source` as text.
+    def create_inbound_email_from_source(source, status: :processing)
       ActionMailbox::InboundEmail.create_and_extract_message_id! source, status: status
     end
 
@@ -23,5 +24,8 @@ module ActionMailbox
     def receive_inbound_email_from_mail(**kwargs)
       create_inbound_email_from_mail(**kwargs).tap(&:route)
     end
+    def receive_inbound_email_from_source(**kwargs)
+      create_inbound_email_from_source(**kwargs).tap(&:route)
+    end
   end
 end
diff --git a/test/unit/inbound_email/message_id_test.rb b/test/unit/inbound_email/message_id_test.rb
index c744a5bf99..1cc3de360e 100644
--- a/test/unit/inbound_email/message_id_test.rb
+++ b/test/unit/inbound_email/message_id_test.rb
@@ -7,7 +7,7 @@ class ActionMailbox::InboundEmail::MessageIdTest < ActiveSupport::TestCase
   end
 
   test "message id is generated if its missing" do
-    inbound_email = create_inbound_email "Date: Fri, 28 Sep 2018 11:08:55 -0700\r\nTo: a@example.com\r\nMime-Version: 1.0\r\nContent-Type: text/plain\r\nContent-Transfer-Encoding: 7bit\r\n\r\nHello!"
+    inbound_email = create_inbound_email_from_source "Date: Fri, 28 Sep 2018 11:08:55 -0700\r\nTo: a@example.com\r\nMime-Version: 1.0\r\nContent-Type: text/plain\r\nContent-Transfer-Encoding: 7bit\r\n\r\nHello!"
     assert_not_nil inbound_email.message_id
   end
 end