add old mode test

Makefile

@@ -3,5 +3,6 @@ MOCHA = node_modules/.bin/mocha
 
 test:
 	$(MOCHA)
+	SIMPLE_LRU_USE_OLD=true $(MOCHA)
 
 .PHONY: test

test/simple-lru.js

@@ -1,6 +1,15 @@
 
 var expect = require('expect.js')
-  , SimpleLRU = require('../')
+var SimpleLRU
+
+if (process.env.SIMPLE_LRU_USE_OLD) {
+  var nativeCreate = Object.create
+  Object.create = undefined
+  SimpleLRU = require('../')
+  Object.create = nativeCreate
+} else {
+  SimpleLRU = require('../')
+}
 
 describe('SimpleLRU', function () {