Extract selecting_no_body? to HTMLSelector.

We're only touching state that the HTMLSelector already knows about in
the method, so just internalize it and nodoc it.

Author: kaspth

lib/rails/dom/testing/assertions/selector_assertions.rb

@@ -166,7 +166,7 @@ def assert_select(*args, &block)
 
           selector = HTMLSelector.new(args, @selected) { nodeset document_root_element }
 
-          if selecting_no_body?(selector)
+          if selector.selecting_no_body?
             assert true
             return
           end
@@ -284,12 +284,6 @@ def assert_size_match!(size, equals, css_selector, message = nil)
             end
           end
 
-          def selecting_no_body?(html_selector)
-            # Nokogiri gives the document a body element. Which means we can't
-            # run an assertion expecting there to not be a body.
-            html_selector.selector == 'body' && html_selector.tests[:count] == 0
-          end
-
           def nest_selection(selection)
             # Set @selected to allow nested assert_select.
             # Can be nested several levels deep.

lib/rails/dom/testing/assertions/selector_assertions/html_selector.rb

@@ -16,6 +16,12 @@ def initialize(values, previous_selection = nil, &root_fallback)
     end
   end
 
+  def selecting_no_body? #:nodoc:
+    # Nokogiri gives the document a body element. Which means we can't
+    # run an assertion expecting there to not be a body.
+    @selector == 'body' && @tests[:count] == 0
+  end
+
   def select
     filter @root.css(selector, context)
   end