make the default environment have actual defaults

instead of deleting keys on every instantiation, create defaults we
actually use.  eventually we can pass an environment in to the request,
and create a new req / res object on each call.

actionpack/lib/action_controller/test_case.rb

@@ -143,6 +143,9 @@ module ActionController
   end
 
   class TestRequest < ActionDispatch::TestRequest #:nodoc:
+    DEFAULT_ENV = ActionDispatch::TestRequest::DEFAULT_ENV.dup
+    DEFAULT_ENV.delete 'PATH_INFO'
+
     def initialize(env = {})
       super
 
@@ -207,6 +210,12 @@ module ActionController
       cookie_jar.update(@set_cookies)
       cookie_jar.recycle!
     end
+
+    private
+
+    def default_env
+      DEFAULT_ENV
+    end
   end
 
   class TestResponse < ActionDispatch::TestResponse
@@ -518,8 +527,6 @@ module ActionController
           @controller ||= klass.new rescue nil
         end
 
-        @request.env.delete('PATH_INFO')
-
         if defined?(@controller) && @controller
           @controller.request = @request
           @controller.params = {}

actionpack/lib/action_dispatch/testing/test_request.rb

@@ -12,7 +12,7 @@ module ActionDispatch
 
     def initialize(env = {})
       env = Rails.application.env_config.merge(env) if defined?(Rails.application) && Rails.application
-      super(DEFAULT_ENV.merge(env))
+      super(default_env.merge(env))
 
       self.host        = 'test.host'
       self.remote_addr = '0.0.0.0'
@@ -69,5 +69,11 @@ module ActionDispatch
     def cookies
       @cookies ||= {}.with_indifferent_access
     end
+
+    private
+
+    def default_env
+      DEFAULT_ENV
+    end
   end
 end