Make `parsed_body` extract parser from the content type.

We're not guaranteed to have a `RequestEncoder` to assign on `get` requests
because we aren't extracting the parser from the response content type.

Until now.

actionpack/CHANGELOG.md

@@ -26,7 +26,7 @@
     class ApiTest < ActionDispatch::IntegrationTest
       test 'creates articles' do
         assert_difference -> { Article.count } do
-          post articles_path, { article: { title: 'Ahoy!' } }, as: :json
+          post articles_path, params: { article: { title: 'Ahoy!' } }, as: :json
         end
 
         assert_equal({ id: Article.last.id, title: 'Ahoy!' }, response.parsed_body)

actionpack/lib/action_dispatch/testing/integration.rb

@@ -381,7 +381,7 @@ def process(method, path, params: nil, headers: nil, env: nil, xhr: false, as: n
           response = _mock_session.last_response
           @response = ActionDispatch::TestResponse.from_response(response)
           @response.request = @request
-          @response.response_parser = request_encoder
+          @response.response_parser = RequestEncoder.parser(@response.content_type)
           @html_document = nil
           @url_options = nil
 
@@ -397,6 +397,8 @@ def build_full_uri(path, env)
         class RequestEncoder # :nodoc:
           @encoders = {}
 
+          attr_reader :response_parser
+
           def initialize(mime_name, param_encoder, response_parser, url_encoded_form = false)
             @mime = Mime[mime_name]
 
@@ -424,8 +426,9 @@ def encode_params(params)
             @param_encoder.call(params)
           end
 
-          def parse_body(body)
-            @response_parser.call(body)
+          def self.parser(content_type)
+            mime = Mime::Type.lookup(content_type)
+            encoder(mime ? mime.ref : nil).response_parser
           end
 
           def self.encoder(name)
@@ -726,7 +729,8 @@ def method_missing(sym, *args, &block)
   #     response_parser: -> body { body }
   #
   # Where `param_encoder` defines how the params should be encoded and
-  # `response_parser` defines how the response body should be parsed.
+  # `response_parser` defines how the response body should be parsed through
+  # `parsed_body`.
   #
   # Consult the Rails Testing Guide for more.
 

actionpack/lib/action_dispatch/testing/test_response.rb

@@ -22,7 +22,7 @@ def self.from_response(response)
     attr_writer :response_parser # :nodoc:
 
     def parsed_body
-      @response_parser.parse_body(body)
+      @parsed_body ||= @response_parser.call(body)
     end
   end
 end

actionpack/test/controller/integration_test.rb

@@ -1171,6 +1171,16 @@ def test_registering_custom_encoder
     Mime::Type.unregister :wibble
   end
 
+  def test_parsed_body_without_as_option
+    with_routing do |routes|
+      routes.draw { get ':action' => FooController }
+
+      get '/foos_json.json', params: { foo: 'heyo' }
+
+      assert_equal({ 'foo' => 'heyo' }, response.parsed_body)
+    end
+  end
+
   private
     def post_to_foos(as:)
       with_routing do |routes|