Merge two tests that needs to initialize Rails before accessing `Rails`

Fixes "NameError: uninitialized constant ApplicationTests::ConfigurationTests::CustomTest::Rails"
when run individually

railties/test/application/configuration/custom_test.rb

@@ -10,7 +10,6 @@ def setup
 
       def teardown
         teardown_app
-        FileUtils.rm_rf(new_app) if File.directory?(new_app)
       end
 
       test "access custom configuration point" do
@@ -30,28 +29,14 @@ def teardown
         assert_equal false, x.hyper_debugger
         assert_nil x.nil_debugger
         assert_nil x.i_do_not_exist.zomg
-      end
 
-      test "custom configuration responds to all messages" do
-        x = Rails.configuration.x
+        # test that custom configuration responds to all messages
         assert_equal true, x.respond_to?(:i_do_not_exist)
         assert_kind_of Method, x.method(:i_do_not_exist)
         assert_kind_of ActiveSupport::OrderedOptions, x.i_do_not_exist
       end
 
       private
-        def new_app
-          File.expand_path("#{app_path}/../new_app")
-        end
-
-        def copy_app
-          FileUtils.cp_r(app_path, new_app)
-        end
-
-        def app
-          @app ||= Rails.application
-        end
-
         def require_environment
           require "#{app_path}/config/environment"
         end