diff --git a/actionpack/lib/action_dispatch/testing/integration.rb b/actionpack/lib/action_dispatch/testing/integration.rb
index a1c2a8858a..c60395acf9 100644
--- a/actionpack/lib/action_dispatch/testing/integration.rb
+++ b/actionpack/lib/action_dispatch/testing/integration.rb
@@ -211,7 +211,7 @@ module ActionDispatch
         end
 
         if path =~ %r{://}
-          path = build_expanded_path(path, request_encoder) do |location|
+          path = build_expanded_path(path) do |location|
             https! URI::HTTPS === location if location.scheme
 
             if url_host = location.host
@@ -220,8 +220,6 @@ module ActionDispatch
               host! url_host
             end
           end
-        elsif as
-          path = build_expanded_path(path, request_encoder)
         end
 
         hostname, port = host.split(":")
@@ -239,7 +237,7 @@ module ActionDispatch
           "HTTP_HOST"      => host,
           "REMOTE_ADDR"    => remote_addr,
           "CONTENT_TYPE"   => request_encoder.content_type,
-          "HTTP_ACCEPT"    => accept
+          "HTTP_ACCEPT"    => request_encoder.accept_header || accept
         }
 
         wrapped_headers = Http::Headers.from_hash({})
@@ -291,10 +289,10 @@ module ActionDispatch
           "#{env['rack.url_scheme']}://#{env['SERVER_NAME']}:#{env['SERVER_PORT']}#{path}"
         end
 
-        def build_expanded_path(path, request_encoder)
+        def build_expanded_path(path)
           location = URI.parse(path)
           yield location if block_given?
-          path = request_encoder.append_format_to location.path
+          path = location.path
           location.query ? "#{path}?#{location.query}" : path
         end
     end
diff --git a/actionpack/lib/action_dispatch/testing/request_encoder.rb b/actionpack/lib/action_dispatch/testing/request_encoder.rb
index b0b994b2d0..734fc8cb54 100644
--- a/actionpack/lib/action_dispatch/testing/request_encoder.rb
+++ b/actionpack/lib/action_dispatch/testing/request_encoder.rb
@@ -1,10 +1,17 @@
 module ActionDispatch
   class RequestEncoder # :nodoc:
-    @encoders = {}
+    class IdentityEncoder
+      def content_type; end
+      def accept_header; end
+      def encode_params(params); params; end
+      def response_parser; -> body { body }; end
+    end
+
+    @encoders = { identity: IdentityEncoder.new }
 
     attr_reader :response_parser
 
-    def initialize(mime_name, param_encoder, response_parser, url_encoded_form = false)
+    def initialize(mime_name, param_encoder, response_parser = nil)
       @mime = Mime[mime_name]
 
       unless @mime
@@ -12,24 +19,18 @@ module ActionDispatch
           "unregistered MIME Type: #{mime_name}. See `Mime::Type.register`."
       end
 
-      @url_encoded_form = url_encoded_form
-      @path_format      = ".#{@mime.symbol}" unless @url_encoded_form
-      @response_parser  = response_parser || -> body { body }
-      @param_encoder    = param_encoder   || :"to_#{@mime.symbol}".to_proc
-    end
-
-    def append_format_to(path)
-      if @url_encoded_form
-        path
-      else
-        path + @path_format
-      end
+      @response_parser = response_parser || -> body { body }
+      @param_encoder   = param_encoder   || :"to_#{@mime.symbol}".to_proc
     end
 
     def content_type
       @mime.to_s
     end
 
+    def accept_header
+      @mime.to_s
+    end
+
     def encode_params(params)
       @param_encoder.call(params)
     end
@@ -40,7 +41,7 @@ module ActionDispatch
     end
 
     def self.encoder(name)
-      @encoders[name] || WWWFormEncoder
+      @encoders[name] || @encoders[:identity]
     end
 
     def self.register_encoder(mime_name, param_encoder: nil, response_parser: nil)
@@ -48,7 +49,5 @@ module ActionDispatch
     end
 
     register_encoder :json, response_parser: -> body { JSON.parse(body) }
-
-    WWWFormEncoder = new(:url_encoded_form, -> params { params }, nil, true)
   end
 end
diff --git a/actionpack/test/controller/integration_test.rb b/actionpack/test/controller/integration_test.rb
index f89cfdb78c..d8be5d32e1 100644
--- a/actionpack/test/controller/integration_test.rb
+++ b/actionpack/test/controller/integration_test.rb
@@ -930,6 +930,10 @@ end
 
 class IntegrationRequestEncodersTest < ActionDispatch::IntegrationTest
   class FooController < ActionController::Base
+    def foos
+      render plain: "ok"
+    end
+
     def foos_json
       render json: params.permit(:foo)
     end
@@ -958,13 +962,30 @@ class IntegrationRequestEncodersTest < ActionDispatch::IntegrationTest
   def test_encoding_as_json
     post_to_foos as: :json do
       assert_response :success
-      assert_match "foos_json.json", request.path
       assert_equal "application/json", request.content_type
+      assert_equal "application/json", request.accepts.first.to_s
+      assert_equal :json, request.format.ref
       assert_equal({ "foo" => "fighters" }, request.request_parameters)
       assert_equal({ "foo" => "fighters" }, response.parsed_body)
     end
   end
 
+  def test_doesnt_mangle_request_path
+    with_routing do |routes|
+      routes.draw do
+        ActiveSupport::Deprecation.silence do
+          post ":action" => FooController
+        end
+      end
+
+      post "/foos"
+      assert_equal "/foos", request.path
+
+      post "/foos_json", as: :json
+      assert_equal "/foos_json", request.path
+    end
+  end
+
   def test_encoding_as_without_mime_registration
     assert_raise ArgumentError do
       ActionDispatch::IntegrationTest.register_encoder :wibble
@@ -979,8 +1000,10 @@ class IntegrationRequestEncodersTest < ActionDispatch::IntegrationTest
 
     post_to_foos as: :wibble do
       assert_response :success
-      assert_match "foos_wibble.wibble", request.path
+      assert_equal "/foos_wibble", request.path
       assert_equal "text/wibble", request.content_type
+      assert_equal "text/wibble", request.accepts.first.to_s
+      assert_equal :wibble, request.format.ref
       assert_equal Hash.new, request.request_parameters # Unregistered MIME Type can't be parsed.
       assert_equal "ok", response.parsed_body
     end