revises a test to account for case-insensitive file systems

The patched test assumed the file system is case-sensitive, but that is not
necessarily the case. In particular, this test did not pass in the recommended
setup for the dev box, because the /vagrant shared folder is case-insensitive.

After looking at some gems that provide access to file system metadata I have
chosen to go with the check you can see in the patch because, albeit it's a bit
dirty creating a file, it is super easy to understand and clearly portable.

References https://github.com/rails/rails-dev-box/issues/102.

actionview/test/actionpack/controller/render_test.rb

@@ -1,5 +1,6 @@
 require 'abstract_unit'
-require "active_model"
+require 'active_model'
+require 'fileutils'
 
 class ApplicationController < ActionController::Base
   self.view_paths = File.join(FIXTURE_LOAD_PATH, "actionpack")
@@ -678,6 +679,14 @@ class RenderTest < ActionController::TestCase
     ActionView::Base.logger = nil
   end
 
+  def case_sensitive_file_system?
+    fname = '.case_sensitive_file_system_test'
+    FileUtils.touch(fname)
+    !File.exists?(fname.upcase)
+  ensure
+    FileUtils.rm_f(fname)
+  end
+
   # :ported:
   def test_simple_show
     get :hello_world
@@ -747,8 +756,15 @@ class RenderTest < ActionController::TestCase
   end
 
   def test_render_action_upcased
-    assert_raise ActionView::MissingTemplate do
+    action = :render_action_upcased_hello_world
-      get :render_action_upcased_hello_world
+
+    if case_sensitive_file_system?
+      assert_raise ActionView::MissingTemplate do
+        get action
+      end
+    else
+      get action
+      assert_template 'test/Hello_world'
     end
   end