assert_select xmlns example does not work

[dnrce]

The example assert_select "feed[xmlns='http://www.w3.org/2005/Atom']" fails against matching XML content. It succeeds when the same body is returned with a text/html content-type.

Gist to reproduce the issue: https://gist.github.com/dnrce/1ce455ef4c3fbfff8fca43dea13da148

This example usage is documented at https://github.com/rails/rails-dom-testing/blob/f94ac0a394bd4cc1f03661005d69b0d69453fbf2/lib/rails/dom/testing/assertions/selector_assertions.rb#L196.

This means the suggested test pattern doesn't work against content generated by AtomFeedHelper: http://api.rubyonrails.org/classes/ActionView/Helpers/AtomFeedHelper.html