Support for the XPath not() function.

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

@@ -0,0 +1,26 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'not() function' do
+    before do
+      @document  = parse('<root>foo</root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return false when the argument is a non-zero integer' do
+      @evaluator.evaluate('not(10)').should == false
+    end
+
+    example 'return true when the argument is a zero integer' do
+      @evaluator.evaluate('not(0)').should == true
+    end
+
+    example 'return false when the argument is a non-empty node set' do
+      @evaluator.evaluate('not(root)').should == false
+    end
+
+    example 'return itrue when the argument is an empty node set' do
+      @evaluator.evaluate('not(foo)').should == true
+    end
+  end
+end