Support for the XPath namespace-uri() function.

spec/oga/xpath/evaluator/calls/namespace_uri_spec.rb

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'namespace-uri() function' do
+    before do
+      @document  = parse('<root xmlns:x="y"><x:a></x:a><b></b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    context 'outside predicates' do
+      example 'return the namespace URI of the <x:a> node' do
+        @evaluator.evaluate('namespace-uri(root/x:a)').should == 'y'
+      end
+
+      example 'return an empty string when there is no namespace URI' do
+        @evaluator.evaluate('namespace-uri(root/b)').should == ''
+      end
+
+      example 'raise TypeError for invalid argument types' do
+        block = lambda { @evaluator.evaluate('namespace-uri("foo")') }
+
+        block.should raise_error(TypeError)
+      end
+    end
+
+    context 'inside predicates' do
+      before do
+        @set = @evaluator.evaluate('root/*[namespace-uri()]')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return the <x:a> node' do
+        @set[0].should == @document.children[0].children[0]
+      end
+    end
+  end
+end