Ok, this is why I added the check  It seems can? does not work well if you are not logged in: 
  1) ContentBlockHelper anonymous should show the content
     Failure/Error: subject { helper.editable_content_block(content_block) }
     NoMethodError:
       undefined method `authenticate' for nil:NilClass
     # ./app/helpers/content_block_helper.rb:4:in `editable_content_block'
     # ./spec/helpers/content_block_helper_spec.rb:6:in `block (2 levels) in <top (required)>'
     # ./spec/helpers/content_block_helper_spec.rb:37:in `block (3 levels) in <top (required)>'