A missing require is added to fix build. When performing rake test:isolated in actionmailer, test/base_test.rb was break.

[kennyj]

I fixed some warnings related to mime_type method's deprecation on master (#7469).

But I got some another problems.
When executing rake test:isolated in ActionMailer, test/base_test.rb was break.

 1) Failure:
test_0007_should set template content type if mail has only one part(BaseTest) [test/base_test.rb:69]:
Expected: "text/html"
Actual: "text/plain"
...

After investigating, I realized the cause of problem.
If we didn't load action_dispatch, we also didn't execute ActionView::Template::Types.delegate_to Mime
Please see also 67f55e2#L0R107.

If we delegate to Mime, build is success.

[kennyj]

cc/ @drogus

[rafaelfranca]

@drogus all yours

[drogus]

Thanks! I'm wondering why tests:isolated are not run on CI, though, is there any good reason to leave them (apart from running time?)

[drogus]

Ok, sorry, disregard my question, I misunderstood what @kennyj was saying