assert_template in Rails3 mailer test

gistfile1.rb

class SomeMailerTest < ActionMailer::TestCase
  # include this so that assert_template is defined
  include ActionController::TemplateAssertions
end
class SomeMailerTest < ActionMailer::TestCase
  test "the mailer" do
    email = SomeMailer.the_mailer.deliver

    assert_template :partial=>'_the_mailer_partial'
  end

  private
  
  def validate_request!
    # this method is added so that assert_template will work
    #
    # overrides method defined in ActionDispatch::Assertions::ResponseAssertions
    # even if you include that module to work around NoMethodError, it won't work b/c @response isn't
    # an ActionDispatch::Request object
  end

end

I had a hard time writing test coverage for a mailer that used a partial template, b/c assert_template doesn't work out-of-the-box in ActionMailer::TestCase.

I hope this saves other people some time and research.