Let TestResponse assign a parser.

Previously we'd only assign a response parser when a request came through
Action Dispatch integration tests. This made calls to `parsed_body` when a TestResponse
was manually instantiated — though own doing or perhaps from a framework — unintentionally
blow up because no parser was set at that time.

The response can lookup a parser entirely through its own ivars. Extract request encoder to
its own file and assume that a viable content type is present at TestResponse instantiation.

Since the default response parser is a no-op, making `parsed_body` equal to `body`, no
exceptions will be thrown.

1 files changed, 7 insertions, 2 deletions

diff --git a/actionpack/lib/action_dispatch/testing/test_response.rb b/actionpack/lib/action_dispatch/testing/test_response.rb
index 9d4b73a43d..bedb7a5558 100644
--- a/actionpack/lib/action_dispatch/testing/test_response.rb
+++ b/actionpack/lib/action_dispatch/testing/test_response.rb
@@ -1,3 +1,5 @@
+require 'action_dispatch/testing/request_encoder'
+
 module ActionDispatch
   # Integration test methods such as ActionDispatch::Integration::Session#get
   # and ActionDispatch::Integration::Session#post return objects of class
@@ -10,6 +12,11 @@ module ActionDispatch
       new response.status, response.headers, response.body
     end
 
+    def initialize(*) # :nodoc:
+      super
+      @response_parser = RequestEncoder.parser(content_type)
+    end
+
     # Was the response successful?
     alias_method :success?, :successful?
 
@@ -19,8 +26,6 @@ module ActionDispatch
     # Was there a server-side error?
     alias_method :error?, :server_error?
 
-    attr_writer :response_parser # :nodoc:
-
     def parsed_body
       @parsed_body ||= @response_parser.call(body)
     end