Support for the XPath comment() test.

lib/oga/xpath/evaluator.rb

@@ -474,6 +474,23 @@ module Oga
         return nodes
       end
 
+      ##
+      # Processes the `comment()` type test. This matches only comment nodes.
+      #
+      # @param [Oga::XPath::Node] ast_node
+      # @param [Oga::XML::NodeSet] context
+      # @return [Oga::XML::NodeSet]
+      #
+      def on_type_test_comment(ast_node, context)
+        nodes = XML::NodeSet.new
+
+        context.each do |node|
+          nodes << node if node.is_a?(XML::Comment)
+        end
+
+        return nodes
+      end
+
       ##
       # Returns a node set containing all the child nodes of the given set of
       # nodes.

spec/oga/xpath/evaluator/type_tests/comment_spec.rb

@@ -0,0 +1,42 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'comment() tests' do
+    before do
+      @document  = parse('<a><!--foo--><b><!--bar--></b></a>')
+      @evaluator = described_class.new(@document)
+    end
+
+    context 'matching text nodes' do
+      before do
+        @set = @evaluator.evaluate('a/comment()')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return a Comment instance' do
+        @set[0].is_a?(Oga::XML::Comment).should == true
+      end
+
+      example 'return the "foo" comment node' do
+        @set[0].text.should == 'foo'
+      end
+    end
+
+    context 'matching nested text nodes' do
+      before do
+        @set = @evaluator.evaluate('a/b/comment()')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return a Comment instance' do
+        @set[0].is_a?(Oga::XML::Comment).should == true
+      end
+
+      example 'return the "bar" comment node' do
+        @set[0].text.should == 'bar'
+      end
+    end
+  end
+end