Speed up view specs

The caching was turned off in [1] because different formats were being
cached under the same key. I believe the need to do this was removed
in the previous commit.

This reduces the time it takes to run FutureLearn’s view specs
by about 50%. I think it’s sensible to use the view cache during
test because it’s normally on between requests in other environments,
and it looks like it was only turned off to work around this caching
issue.

[1] rspec#864

Author: zetter

lib/rspec/rails/example/view_example_group.rb

@@ -155,9 +155,6 @@ def _include_controller_helpers
             view.lookup_context.prefixes << _controller_path
           end
 
-          # fixes bug with differing formats
-          view.lookup_context.view_paths.each(&:clear_cache)
-
           controller.controller_path = _controller_path
           controller.request.path_parameters[:controller] = _controller_path
           controller.request.path_parameters[:action]     = _inferred_action unless _inferred_action =~ /^_/