Added a testcase for bug [#5329]

Signed-off-by: José Valim <jose.valim@gmail.com>

actionmailer/test/fixtures/i18n_test_mailer/mail_with_i18n_subject.erb

@@ -0,0 +1,4 @@
+Hello there,
+
+Mr. <%= @recipient %>.  Be greeted, new member!
+

actionmailer/test/i18n_with_controller_test.rb

@@ -0,0 +1,50 @@
+require 'abstract_unit'
+require 'action_controller'
+
+class I18nTestMailer < ActionMailer::Base
+
+  configure do |c|
+    c.assets_dir = '' # To get the tests to pass
+  end
+
+  def mail_with_i18n_subject(recipient)
+    @recipient   = recipient
+    I18n.locale = :de
+    mail(:to => recipient, :subject => "#{I18n.t :email_subject} #{recipient}",
+      :from => "system@loudthinking.com", :date => Time.local(2004, 12, 12))
+  end
+end
+
+class TestController < ActionController::Base
+  def send_mail
+    I18nTestMailer.mail_with_i18n_subject(@recipient).deliver
+    render :text => 'Mail sent'
+  end
+end
+
+class ActionMailerI18nWithControllerTest < ActionDispatch::IntegrationTest
+
+  Routes = ActionDispatch::Routing::RouteSet.new
+  Routes.draw do
+    match ':controller(/:action(/:id))'
+  end
+
+  def app
+    Routes
+  end
+
+  def setup
+    I18n.backend.store_translations('de', :email_subject => '[Signed up] Welcome')
+    set_delivery_method :test
+    ActionMailer::Base.perform_deliveries = true
+    ActionMailer::Base.deliveries.clear
+    ActiveSupport::Deprecation.silenced = false
+
+    @recipient = 'test@localhost'
+  end
+
+  def test_send_mail
+    get '/test/send_mail'
+    assert_equal "Mail sent", @response.body
+  end
+end