Include namespaces when converting attrs to XML.

lib/oga/xml/attribute.rb

@@ -81,7 +81,13 @@ module Oga
       # @return [String]
       #
       def to_xml
-        return %Q(#{name}="#{value}")
+        if namespace_name
+          full_name = "#{namespace.name}:#{name}"
+        else
+          full_name = name
+        end
+
+        return %Q(#{full_name}="#{value}")
       end
 
       ##

spec/oga/xml/attribute_spec.rb

@@ -48,11 +48,26 @@ describe Oga::XML::Attribute do
   end
 
   context '#to_xml' do
-    example 'return a key/value pair for an XML document' do
+    example 'convert an attribute to XML' do
       attr = described_class.new(:name => 'foo', :value => 'bar')
 
       attr.to_xml.should == 'foo="bar"'
     end
+
+    example 'include the namespace when converting an attribute to XML' do
+      element = Oga::XML::Element.new
+
+      element.register_namespace('foo', 'http://foo')
+
+      attr = described_class.new(
+        :name           => 'class',
+        :namespace_name => 'foo',
+        :value          => '10',
+        :element        => element
+      )
+
+      attr.to_xml.should == 'foo:class="10"'
+    end
   end
 
   context '#inspect' do