Update test files.

test/mailers/confirmation_instructions_plain_text_test.rb

@@ -1,30 +0,0 @@
-require 'test/test_helper'
-
-class ConfirmationInstructionsPlainTextTest < ActionMailer::TestCase
-
-  def setup
-    setup_mailer
-    Devise.mailer_sender       = 'test@example.com'
-    Devise.mailer_content_type = 'text/plain'
-  end
-  
-  def teardown
-    Devise.mailer_content_type = 'text/html' # the default
-  end
-
-  def user
-    @user ||= create_user
-  end
-
-  def mail
-    @mail ||= begin
-      user
-      ActionMailer::Base.deliveries.first
-    end
-  end
-
-  test 'content type should be set to plain when manually configured' do
-    assert_equal 'text/plain', mail.content_type
-  end
-
-end

test/mailers/confirmation_instructions_test.rb

@@ -63,6 +63,12 @@ class ConfirmationInstructionsTest < ActionMailer::TestCase
     end
   end
 
+  test 'content type should be set to plain when manually configured' do
+    swap Devise, :mailer_content_type => "text/plain" do
+      assert_equal "text/plain", mail.content_type
+    end
+  end
+
   test 'renders a scoped if scoped_views is set in the mailer class' do
     begin
       DeviseMailer.scoped_views = true