Inherit from ActionMailer::TestCase

test/mailers/contact_mailer_test.rb

@@ -1,11 +1,8 @@
 require 'test_helper'
 
-class ContactMailerTest < ActiveSupport::TestCase
-  include ActionMailer::TestHelper
-
+class ContactMailerTest < ActionMailer::TestCase
   setup do
     @contact = contacts(:john)
-    ActionMailer::Base.deliveries.clear
   end
 
   def test_delivers_email_changed_email

test/mailers/domain_delete_mailer_test.rb

@@ -1,11 +1,8 @@
 require 'test_helper'
 
-class DomainDeleteMailerTest < ActiveSupport::TestCase
-  include ActionMailer::TestHelper
-
+class DomainDeleteMailerTest < ActionMailer::TestCase
   setup do
     @domain = domains(:shop)
-    ActionMailer::Base.deliveries.clear
   end
 
   def test_force_delete_templates

test/mailers/domain_expire_mailer_test.rb

@@ -1,12 +1,6 @@
 require 'test_helper'
 
-class DomainExpireMailerTest < ActiveSupport::TestCase
-  include ActionMailer::TestHelper
-
-  setup do
-    ActionMailer::Base.deliveries.clear
-  end
-
+class DomainExpireMailerTest < ActionMailer::TestCase
   def test_delivers_domain_expiration_email
     domain = domains(:shop)
     assert_equal 'shop.test', domain.name

test/mailers/invoice_mailer_test.rb

@@ -1,11 +1,8 @@
 require 'test_helper'
 
-class InvoiceMailerTest < ActiveSupport::TestCase
-  include ActionMailer::TestHelper
-
+class InvoiceMailerTest < ActionMailer::TestCase
   setup do
     @invoice = invoices(:one)
-    ActionMailer::Base.deliveries.clear
   end
 
   def test_delivers_invoice_email

test/mailers/registrant_change_mailer_test.rb

@@ -1,11 +1,8 @@
 require 'test_helper'
 
-class RegistrantChangeMailerTest < ActiveSupport::TestCase
-  include ActionMailer::TestHelper
-
+class RegistrantChangeMailerTest < ActionMailer::TestCase
   setup do
     @domain = domains(:shop)
-    ActionMailer::Base.deliveries.clear
   end
 
   def test_delivers_confirmation_request_email