Merge pull request #4 from dixpac/dix/add_frozen_string_literals

Add frozen_string_literal: true to match Rails codebase

51 files changed, 102 insertions, 0 deletions

diff --git a/app/controllers/action_mailbox/base_controller.rb b/app/controllers/action_mailbox/base_controller.rb
index b73f5b7708..f8764a8240 100644
--- a/app/controllers/action_mailbox/base_controller.rb
+++ b/app/controllers/action_mailbox/base_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # The base class for all Active Mailbox ingress controllers.
 class ActionMailbox::BaseController < ActionController::Base
   skip_forgery_protection
diff --git a/app/controllers/action_mailbox/ingresses/amazon/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/amazon/inbound_emails_controller.rb
index 0c04170eae..2a8ec375c7 100644
--- a/app/controllers/action_mailbox/ingresses/amazon/inbound_emails_controller.rb
+++ b/app/controllers/action_mailbox/ingresses/amazon/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ingests inbound emails from Amazon's Simple Email Service (SES).
 #
 # Requires the full RFC 822 message in the +content+ parameter. Authenticates requests by validating their signatures.
diff --git a/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb
index 7583e25f26..225bcc5565 100644
--- a/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb
+++ b/app/controllers/action_mailbox/ingresses/mailgun/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ingests inbound emails from Mailgun. Requires the following parameters:
 #
 # - +body-mime+: The full RFC 822 message
diff --git a/app/controllers/action_mailbox/ingresses/mandrill/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/mandrill/inbound_emails_controller.rb
index 8be27009d2..5a85e6b7f0 100644
--- a/app/controllers/action_mailbox/ingresses/mandrill/inbound_emails_controller.rb
+++ b/app/controllers/action_mailbox/ingresses/mandrill/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ingests inbound emails from Mandrill.
 #
 # Requires a +mandrill_events+ parameter containing a JSON array of Mandrill inbound email event objects.
diff --git a/app/controllers/action_mailbox/ingresses/postfix/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/postfix/inbound_emails_controller.rb
index ba04effd1f..a3b794c65b 100644
--- a/app/controllers/action_mailbox/ingresses/postfix/inbound_emails_controller.rb
+++ b/app/controllers/action_mailbox/ingresses/postfix/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ingests inbound emails relayed from Postfix.
 #
 # Authenticates requests using HTTP basic access authentication. The username is always +actionmailbox+, and the
diff --git a/app/controllers/action_mailbox/ingresses/sendgrid/inbound_emails_controller.rb b/app/controllers/action_mailbox/ingresses/sendgrid/inbound_emails_controller.rb
index 8e1d781c2c..c48abae66c 100644
--- a/app/controllers/action_mailbox/ingresses/sendgrid/inbound_emails_controller.rb
+++ b/app/controllers/action_mailbox/ingresses/sendgrid/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ingests inbound emails from SendGrid. Requires an +email+ parameter containing a full RFC 822 message.
 #
 # Authenticates requests using HTTP basic access authentication. The username is always +actionmailbox+, and the
diff --git a/app/controllers/rails/conductor/action_mailbox/inbound_emails_controller.rb b/app/controllers/rails/conductor/action_mailbox/inbound_emails_controller.rb
index 9804f6ec5b..eb96d88691 100644
--- a/app/controllers/rails/conductor/action_mailbox/inbound_emails_controller.rb
+++ b/app/controllers/rails/conductor/action_mailbox/inbound_emails_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Rails::Conductor::ActionMailbox::InboundEmailsController < Rails::Conductor::BaseController
   def index
     @inbound_emails = ActionMailbox::InboundEmail.order(created_at: :desc)
diff --git a/app/controllers/rails/conductor/action_mailbox/reroutes_controller.rb b/app/controllers/rails/conductor/action_mailbox/reroutes_controller.rb
index 6191bda5e5..c53203049b 100644
--- a/app/controllers/rails/conductor/action_mailbox/reroutes_controller.rb
+++ b/app/controllers/rails/conductor/action_mailbox/reroutes_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Rerouting will run routing and processing on an email that has already been, or attempted to be, processed.
 class Rails::Conductor::ActionMailbox::ReroutesController < Rails::Conductor::BaseController
   def create
diff --git a/app/controllers/rails/conductor/base_controller.rb b/app/controllers/rails/conductor/base_controller.rb
index cfa0b84963..c95a7f3b93 100644
--- a/app/controllers/rails/conductor/base_controller.rb
+++ b/app/controllers/rails/conductor/base_controller.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # TODO: Move this to Rails::Conductor gem
 class Rails::Conductor::BaseController < ActionController::Base
   layout "rails/conductor"
diff --git a/app/jobs/action_mailbox/incineration_job.rb b/app/jobs/action_mailbox/incineration_job.rb
index 3c6c9aae4f..27dd9b151f 100644
--- a/app/jobs/action_mailbox/incineration_job.rb
+++ b/app/jobs/action_mailbox/incineration_job.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # You can configure when this `IncinerationJob` will be run as a time-after-processing using the
 # `config.action_mailbox.incinerate_after` or `ActionMailbox.incinerate_after` setting.
 #
diff --git a/app/jobs/action_mailbox/routing_job.rb b/app/jobs/action_mailbox/routing_job.rb
index c345227617..fc3388daff 100644
--- a/app/jobs/action_mailbox/routing_job.rb
+++ b/app/jobs/action_mailbox/routing_job.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Routing a new InboundEmail is an asynchronous operation, which allows the ingress controllers to quickly
 # accept new incoming emails without being burdened to hang while they're actually being processed.
 class ActionMailbox::RoutingJob < ActiveJob::Base
diff --git a/app/models/action_mailbox/inbound_email.rb b/app/models/action_mailbox/inbound_email.rb
index 156e2d4dbc..d815941922 100644
--- a/app/models/action_mailbox/inbound_email.rb
+++ b/app/models/action_mailbox/inbound_email.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "mail"
 
 # The `InboundEmail` is an Active Record that keeps a reference to the raw email stored in Active Storage
diff --git a/app/models/action_mailbox/inbound_email/incineratable.rb b/app/models/action_mailbox/inbound_email/incineratable.rb
index a049b88b69..fb2461cf50 100644
--- a/app/models/action_mailbox/inbound_email/incineratable.rb
+++ b/app/models/action_mailbox/inbound_email/incineratable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Ensure that the `InboundEmail` is automatically scheduled for later incineration if the status has been
 # changed to `processed`. The later incineration will be invoked at the time specified by the 
 # `ActionMailbox.incinerate_after` time using the `IncinerationJob`.
diff --git a/app/models/action_mailbox/inbound_email/incineratable/incineration.rb b/app/models/action_mailbox/inbound_email/incineratable/incineration.rb
index 50861bc64b..c4aaaa25a9 100644
--- a/app/models/action_mailbox/inbound_email/incineratable/incineration.rb
+++ b/app/models/action_mailbox/inbound_email/incineratable/incineration.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Command class for carrying out the actual incineration of the `InboundMail` that's been scheduled 
 # for removal. Before the incineration – which really is just a call to `#destroy!` – is run, we verify
 # that it's both eligible (by virtue of having already been processed) and time to do so (that is, 
diff --git a/app/models/action_mailbox/inbound_email/message_id.rb b/app/models/action_mailbox/inbound_email/message_id.rb
index dc17e48e74..4807a2a293 100644
--- a/app/models/action_mailbox/inbound_email/message_id.rb
+++ b/app/models/action_mailbox/inbound_email/message_id.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # The `Message-ID` as specified by rfc822 is supposed to be a unique identifier for that individual email. 
 # That makes it an ideal tracking token for debugging and forensics, just like `X-Request-Id` does for 
 # web request.
diff --git a/app/models/action_mailbox/inbound_email/routable.rb b/app/models/action_mailbox/inbound_email/routable.rb
index f042fa4f57..58d67eb20c 100644
--- a/app/models/action_mailbox/inbound_email/routable.rb
+++ b/app/models/action_mailbox/inbound_email/routable.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # A newly received `InboundEmail` will not be routed synchronously as part of ingress controller's receival.
 # Instead, the routing will be done asynchronously, using a `RoutingJob`, to ensure maximum parallel capacity.
 #
diff --git a/lib/action_mailbox.rb b/lib/action_mailbox.rb
index aec2db7b05..578e04a422 100644
--- a/lib/action_mailbox.rb
+++ b/lib/action_mailbox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "action_mailbox/engine"
 require "action_mailbox/mail_ext"
 
diff --git a/lib/action_mailbox/base.rb b/lib/action_mailbox/base.rb
index 0ae83bf691..b78110d039 100644
--- a/lib/action_mailbox/base.rb
+++ b/lib/action_mailbox/base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "active_support/rescuable"
 
 require "action_mailbox/callbacks"
diff --git a/lib/action_mailbox/callbacks.rb b/lib/action_mailbox/callbacks.rb
index f1bbd0593d..c6f07d7ccf 100644
--- a/lib/action_mailbox/callbacks.rb
+++ b/lib/action_mailbox/callbacks.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "active_support/callbacks"
 
 module ActionMailbox
diff --git a/lib/action_mailbox/engine.rb b/lib/action_mailbox/engine.rb
index e0954e4e49..8b010826e9 100644
--- a/lib/action_mailbox/engine.rb
+++ b/lib/action_mailbox/engine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "rails/engine"
 
 module ActionMailbox
diff --git a/lib/action_mailbox/mail_ext.rb b/lib/action_mailbox/mail_ext.rb
index abdaae4f9e..c4d277a1f9 100644
--- a/lib/action_mailbox/mail_ext.rb
+++ b/lib/action_mailbox/mail_ext.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "mail"
 
 # The hope is to upstream most of these basic additions to the Mail gem's Mail object. But until then, here they lay!
diff --git a/lib/action_mailbox/mail_ext/address_equality.rb b/lib/action_mailbox/mail_ext/address_equality.rb
index 76675365dd..69243a666e 100644
--- a/lib/action_mailbox/mail_ext/address_equality.rb
+++ b/lib/action_mailbox/mail_ext/address_equality.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Mail::Address
   def ==(other_address)
     other_address.is_a?(Mail::Address) && to_s == other_address.to_s
diff --git a/lib/action_mailbox/mail_ext/address_wrapping.rb b/lib/action_mailbox/mail_ext/address_wrapping.rb
index f41087a450..fcdfbb6f6f 100644
--- a/lib/action_mailbox/mail_ext/address_wrapping.rb
+++ b/lib/action_mailbox/mail_ext/address_wrapping.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Mail::Address
   def self.wrap(address)
     address.is_a?(Mail::Address) ? address : Mail::Address.new(address)
diff --git a/lib/action_mailbox/mail_ext/addresses.rb b/lib/action_mailbox/mail_ext/addresses.rb
index f64c3ef5df..377373bee6 100644
--- a/lib/action_mailbox/mail_ext/addresses.rb
+++ b/lib/action_mailbox/mail_ext/addresses.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Mail::Message
   def from_address
     header[:from]&.address_list&.addresses&.first
diff --git a/lib/action_mailbox/mail_ext/from_source.rb b/lib/action_mailbox/mail_ext/from_source.rb
index ddc3cbe385..17b7fc80ad 100644
--- a/lib/action_mailbox/mail_ext/from_source.rb
+++ b/lib/action_mailbox/mail_ext/from_source.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Mail
   def self.from_source(source)
     Mail.new Mail::Utilities.binary_unsafe_to_crlf(source.to_s)
diff --git a/lib/action_mailbox/mail_ext/recipients.rb b/lib/action_mailbox/mail_ext/recipients.rb
index 87255ce6ce..a8ac42d602 100644
--- a/lib/action_mailbox/mail_ext/recipients.rb
+++ b/lib/action_mailbox/mail_ext/recipients.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Mail::Message
   def recipients
     Array(to) + Array(cc) + Array(bcc) + Array(header[:x_original_to]).map(&:to_s)
diff --git a/lib/action_mailbox/router.rb b/lib/action_mailbox/router.rb
index ef55718974..0f041a8389 100644
--- a/lib/action_mailbox/router.rb
+++ b/lib/action_mailbox/router.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Encapsulates the routes that live on the ApplicationMailbox and performs the actual routing when
 # an inbound_email is received.
 class ActionMailbox::Router
diff --git a/lib/action_mailbox/router/route.rb b/lib/action_mailbox/router/route.rb
index 6472b9a31d..adb9f94c1a 100644
--- a/lib/action_mailbox/router/route.rb
+++ b/lib/action_mailbox/router/route.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Encapsulates a route, which can then be matched against an inbound_email and provide a lookup of the matching
 # mailbox class. See examples for the different route addresses and how to use them in the `ActionMailbox::Base`
 # documentation.
diff --git a/lib/action_mailbox/routing.rb b/lib/action_mailbox/routing.rb
index db462e6019..1ea96c8a9d 100644
--- a/lib/action_mailbox/routing.rb
+++ b/lib/action_mailbox/routing.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActionMailbox
   # See `ActionMailbox::Base` for how to specify routing.
   module Routing
diff --git a/lib/action_mailbox/test_case.rb b/lib/action_mailbox/test_case.rb
index 1b3aec1393..a501e8a7ca 100644
--- a/lib/action_mailbox/test_case.rb
+++ b/lib/action_mailbox/test_case.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "action_mailbox/test_helper"
 require "active_support/test_case"
 
diff --git a/lib/action_mailbox/test_helper.rb b/lib/action_mailbox/test_helper.rb
index 4e4552629a..02c52fb779 100644
--- a/lib/action_mailbox/test_helper.rb
+++ b/lib/action_mailbox/test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "mail"
 
 module ActionMailbox
diff --git a/lib/action_mailbox/version.rb b/lib/action_mailbox/version.rb
index 23c615dbbd..7e6bd414e8 100644
--- a/lib/action_mailbox/version.rb
+++ b/lib/action_mailbox/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActionMailbox
   VERSION = '0.1.0'
 end
diff --git a/lib/templates/mailboxes/application_mailbox.rb b/lib/templates/mailboxes/application_mailbox.rb
index 9386f9eb91..7a2ed6b2ac 100644
--- a/lib/templates/mailboxes/application_mailbox.rb
+++ b/lib/templates/mailboxes/application_mailbox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ApplicationMailbox < ActionMailbox::Base
   # route /something/i => :somewhere
 end
diff --git a/test/controllers/ingresses/amazon/inbound_emails_controller_test.rb b/test/controllers/ingresses/amazon/inbound_emails_controller_test.rb
index c36c500cbe..e10985553e 100644
--- a/test/controllers/ingresses/amazon/inbound_emails_controller_test.rb
+++ b/test/controllers/ingresses/amazon/inbound_emails_controller_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "test_helper"
 
 ActionMailbox::Ingresses::Amazon::InboundEmailsController.verifier =
diff --git a/test/controllers/ingresses/mailgun/inbound_emails_controller_test.rb b/test/controllers/ingresses/mailgun/inbound_emails_controller_test.rb
index c5ec71013e..3f225b8953 100644
--- a/test/controllers/ingresses/mailgun/inbound_emails_controller_test.rb
+++ b/test/controllers/ingresses/mailgun/inbound_emails_controller_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "test_helper"
 
 ENV["MAILGUN_INGRESS_API_KEY"] = "tbsy84uSV1Kt3ZJZELY2TmShPRs91E3yL4tzf96297vBCkDWgL"
diff --git a/test/controllers/ingresses/mandrill/inbound_emails_controller_test.rb b/test/controllers/ingresses/mandrill/inbound_emails_controller_test.rb
index c8a8e731d6..40f956c930 100644
--- a/test/controllers/ingresses/mandrill/inbound_emails_controller_test.rb
+++ b/test/controllers/ingresses/mandrill/inbound_emails_controller_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "test_helper"
 
 ENV["MANDRILL_INGRESS_API_KEY"] = "1l9Qf7lutEf7h73VXfBwhw"
diff --git a/test/controllers/ingresses/postfix/inbound_emails_controller_test.rb b/test/controllers/ingresses/postfix/inbound_emails_controller_test.rb
index 5e0777aa30..d646f5e859 100644
--- a/test/controllers/ingresses/postfix/inbound_emails_controller_test.rb
+++ b/test/controllers/ingresses/postfix/inbound_emails_controller_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "test_helper"
 
 class ActionMailbox::Ingresses::Postfix::InboundEmailsControllerTest < ActionDispatch::IntegrationTest
diff --git a/test/controllers/ingresses/sendgrid/inbound_emails_controller_test.rb b/test/controllers/ingresses/sendgrid/inbound_emails_controller_test.rb
index 0c7d0d6846..59a87e9248 100644
--- a/test/controllers/ingresses/sendgrid/inbound_emails_controller_test.rb
+++ b/test/controllers/ingresses/sendgrid/inbound_emails_controller_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "test_helper"
 
 class ActionMailbox::Ingresses::Sendgrid::InboundEmailsControllerTest < ActionDispatch::IntegrationTest
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 31fc59bba2..d0d802fdb5 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ENV["RAILS_ENV"] = "test"
 ENV["RAILS_INBOUND_EMAIL_PASSWORD"] = "tbsy84uSV1Kt3ZJZELY2TmShPRs91E3yL4tzf96297vBCkDWgL"
 
diff --git a/test/unit/inbound_email/incineration_test.rb b/test/unit/inbound_email/incineration_test.rb
index b46101bcc4..bcaee16de4 100644
--- a/test/unit/inbound_email/incineration_test.rb
+++ b/test/unit/inbound_email/incineration_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class ActionMailbox::InboundEmail::IncinerationTest < ActiveSupport::TestCase
diff --git a/test/unit/inbound_email/message_id_test.rb b/test/unit/inbound_email/message_id_test.rb
index 1cc3de360e..00e65614ec 100644
--- a/test/unit/inbound_email/message_id_test.rb
+++ b/test/unit/inbound_email/message_id_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class ActionMailbox::InboundEmail::MessageIdTest < ActiveSupport::TestCase
diff --git a/test/unit/inbound_email_test.rb b/test/unit/inbound_email_test.rb
index 7c42188584..42349bc7b4 100644
--- a/test/unit/inbound_email_test.rb
+++ b/test/unit/inbound_email_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../test_helper'
 
 module ActionMailbox
diff --git a/test/unit/mail_ext/address_equality_test.rb b/test/unit/mail_ext/address_equality_test.rb
index 56e9bfa47f..7ea4360b76 100644
--- a/test/unit/mail_ext/address_equality_test.rb
+++ b/test/unit/mail_ext/address_equality_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 module MailExt
diff --git a/test/unit/mail_ext/address_wrapping_test.rb b/test/unit/mail_ext/address_wrapping_test.rb
index 6baa360f3e..a9ae820e26 100644
--- a/test/unit/mail_ext/address_wrapping_test.rb
+++ b/test/unit/mail_ext/address_wrapping_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 module MailExt
diff --git a/test/unit/mail_ext/recipients_test.rb b/test/unit/mail_ext/recipients_test.rb
index e39e1eb89c..4730896354 100644
--- a/test/unit/mail_ext/recipients_test.rb
+++ b/test/unit/mail_ext/recipients_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 module MailExt
diff --git a/test/unit/mailbox/bouncing_test.rb b/test/unit/mailbox/bouncing_test.rb
index 6ac806ba29..ce5de36ff6 100644
--- a/test/unit/mailbox/bouncing_test.rb
+++ b/test/unit/mailbox/bouncing_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class BouncingWithReplyMailbox < ActionMailbox::Base
diff --git a/test/unit/mailbox/callbacks_test.rb b/test/unit/mailbox/callbacks_test.rb
index 279bf7e574..ae720155cf 100644
--- a/test/unit/mailbox/callbacks_test.rb
+++ b/test/unit/mailbox/callbacks_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class CallbackMailbox < ActionMailbox::Base
diff --git a/test/unit/mailbox/routing_test.rb b/test/unit/mailbox/routing_test.rb
index f30199b7af..a83fbdacf2 100644
--- a/test/unit/mailbox/routing_test.rb
+++ b/test/unit/mailbox/routing_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class ApplicationMailbox < ActionMailbox::Base
diff --git a/test/unit/mailbox/state_test.rb b/test/unit/mailbox/state_test.rb
index 32d16ca8fe..78b7d21cd7 100644
--- a/test/unit/mailbox/state_test.rb
+++ b/test/unit/mailbox/state_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 
 class SuccessfulMailbox < ActionMailbox::Base
diff --git a/test/unit/postfix_relayer_test.rb b/test/unit/postfix_relayer_test.rb
index 9d6e49dee3..b448bf6f9b 100644
--- a/test/unit/postfix_relayer_test.rb
+++ b/test/unit/postfix_relayer_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../test_helper'
 
 require 'action_mailbox/postfix_relayer'
diff --git a/test/unit/router_test.rb b/test/unit/router_test.rb
index 70d39ba6a1..ec60fb0889 100644
--- a/test/unit/router_test.rb
+++ b/test/unit/router_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../test_helper'
 
 class RootMailbox < ActionMailbox::Base