Allow setting of request CONTENT-TYPE with as: in controller tests

[everestmz]

Summary

Adds the option for specifications such as as: :json to set the request header, for get, post,... etc methods in controller tests.

For example: post :action, params: { ... }, as: :json sets the CONTENT-TYPE of the request to application/json.

r? @rafaelfranca

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[rafaelfranca]

Could you add a test for this feature in https://github.com/rails/rails/blob/master/actionpack/test/controller/test_case_test.rb?

It will be something like https://github.com/rails/rails/blob/master/actionpack/test/controller/test_case_test.rb#L640-L647, but we will need to assert the Content type and if the parameters where parsed using the content type provided.

[everestmz]

Added a test case for this 👍

[rafaelfranca]

could you squash your commits and a CHANGELOG entry on top of https://github.com/rails/rails/blob/master/actionpack/CHANGELOG.md?

[rafaelfranca]

Oh, forgot about the documentation. Could you update the process documentation to talk about this option?

[matthewd]

Does this do more than making the option shorter to type? 😕

I'm slightly concerned that it creates a parallel in the APIs that isn't supported by the implementations. cc @kaspth

[rafaelfranca]

Does this do more than making the option shorter to type? 😕

Yes, it actually set the content type. ActionController::TestCase doesn't support setting the content type in the process method you have to explicitly set the request.content_type. In Rails 4.2 it worked fine because we were not using the same request object that we use in real requests, now it doesn't work anymore and you have to set the content type if you want your parameters to be parsed as a JSON request.

We already have :as option in ActionDispatch::IntegrationTest, so we are just using the same API here.

[everestmz]

Documentation & changelog updated as well!

[javierjulio]

@rafaelfranca thanks for the update and continuing to see this through! Great work @evmunro! This will hopefully make it easier for those upgrading to Rails 5 from 4.2 since I was spending a lot of time tackling this issue. Thanks ❤️

[rafaelfranca]

To give context why this change is needed:

Since c546a2b, ActionController::TestCase is doing the encoding/decoding roundtrip in the parameters. Before it was just using the same arguments that was given to the methods. Now, the way the parameters are decoded depends on the mime type of the request. This means that in 5.0 the code that worked in 4.2 may not work anymore because we default to 'application/x-www-form-urlencoded' mime type and the test was expecting the json roading trip.

To fix this in Rails 5.0.0 you have to set the request's content type by hand. While this is an acceptable solution it is too cumbersome. ActionDispatch::IntegrationTest already has the :as option to set the mime type that will be used to do the parameter parsing so we are adding the same option to ActionController::TestCase.

[rafaelfranca]

Backported in 09d313a

[tak1n]

@evmunro, @rafaelfranca awesome thanks! ❤️

[kaspth]

Neat! As long as we also make @response.parsed_body work, I think we're good.

It depends on us having a content type at the time we create the response class:

rails/actionpack/lib/action_dispatch/testing/test_response.rb

Line 17 in c1d612c

@response_parser = RequestEncoder.parser(content_type)

rails/actionpack/lib/action_controller/test_case.rb

Line 622 in c1d612c

klass.create