Do not do assertions on mail class.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8991 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/functional/files_controller_test.rb

@@ -72,7 +72,7 @@ class FilesControllerTest < ActionController::TestCase
     assert_equal Project.find(1), a.container
 
     mail = ActionMailer::Base.deliveries.last
-    assert_kind_of TMail::Mail, mail
+    assert_not_nil mail
     assert_equal "[eCookbook] New file", mail.subject
     assert mail.body.include?('testfile.txt')
   end