Flush Element#namespace cache

When setting a new namespace name using Element#namespace_name= the
cache used by Element#namespace is flushed properly.

lib/oga/xml/element.rb

@@ -8,7 +8,7 @@ module Oga
     #  The name of the element.
     #  @return [String]
     #
-    # @!attribute [ww] namespace_name
+    # @!attribute [r] namespace_name
     #  The name of the namespace.
     #  @return [String]
     #
@@ -23,7 +23,9 @@ module Oga
     class Element < Node
       include Querying
 
-      attr_accessor :name, :namespace_name, :attributes
+      attr_reader :namespace_name
+
+      attr_accessor :name, :attributes
 
       attr_writer :namespaces
 
@@ -56,6 +58,14 @@ module Oga
         register_namespaces_from_attributes
       end
 
+      ##
+      # @param [String] name
+      #
+      def namespace_name=(name)
+        @namespace_name = name
+        @namespace      = nil
+      end
+
       ##
       # Returns an attribute matching the given name (with or without the
       # namespace).

spec/oga/xml/element_spec.rb

@@ -42,6 +42,16 @@ describe Oga::XML::Element do
     end
   end
 
+  describe '#namespace_name=' do
+    it 'sets the namepace name' do
+      element = described_class.new(:name => 'a')
+
+      element.namespace_name = 'foo'
+
+      element.namespace_name.should == 'foo'
+    end
+  end
+
   describe '#attribute' do
     before do
       attributes = [
@@ -209,6 +219,17 @@ describe Oga::XML::Element do
       element.namespace.should == namespace
     end
 
+    it 'flushes the cache when changing the namespace name' do
+      namespace = Oga::XML::Namespace.new(:name => 'bar')
+      element   = described_class.new(
+        :namespaces => {'bar' => namespace}
+      )
+
+      element.namespace_name = 'foo'
+
+      element.namespace.should be_nil
+    end
+
     describe 'in an HTML document' do
       it 'returns nil' do
         ns  = Oga::XML::Namespace.new(:name => 'xmlns')