Added XPath::Compiler.compile_with_cache

spec/oga/xpath/compiler_spec.rb

@@ -5,6 +5,32 @@ describe Oga::XPath::Compiler do
     @compiler = described_class.new
   end
 
+  describe 'compile_with_cache' do
+    before do
+      described_class::CACHE.clear
+    end
+
+    it 'returns a Proc as a lambda' do
+      ast   = parse_xpath('foo')
+      block = described_class.compile_with_cache(ast)
+
+      block.should be_an_instance_of(Proc)
+      block.lambda?.should == true
+    end
+
+    it 'caches a compiled Proc' do
+      ast = parse_xpath('foo')
+
+      described_class.any_instance
+        .should_receive(:compile)
+        .once
+        .and_call_original
+
+      described_class.compile_with_cache(ast).should be_an_instance_of(Proc)
+      described_class.compile_with_cache(ast).should be_an_instance_of(Proc)
+    end
+  end
+
   describe '#compile' do
     it 'returns a Proc as a lambda' do
       ast   = parse_xpath('foo')
@@ -21,10 +47,6 @@ describe Oga::XPath::Compiler do
       @compiler.compile(ast).arity.should == 1
     end
 
-    xit 'caches a compiled Proc for a given XPath AST' do
-      # TODO
-    end
-
     describe 'calling the compiled Proc' do
       it 'returns a NodeSet' do
         doc   = parse('<foo></foo>')