rails/rails — pull request #15544 by zuhao (2014-06-06 16:13:01+00:00)
Title: Restore test deliveries properly in ActionMailer.

`ActionMailer::Base.delivery_method` and
`ActionMailer::Base.perform_deliveries` have leaked states.

"delivery method can be customized per instance" and "delivery method
can be customized in subclasses not changing the parent" in
delivery_methods_test.rb will fail if test_helper_test.rb (in which
`TestHelperMailerTest` is inherited from `ActionMailer::TestCase`) runs
before it.

cc @senny this is state leak across test suites.