test the arguments shim and properly factor out the arguments handling

index.js

@@ -7,6 +7,7 @@ var Object_keys = typeof Object.keys === 'function'
         return keys;
     }
 ;
+var isArguments = require('./lib/is_arguments.js');
 
 var deepEqual = module.exports = function (actual, expected, opts) {
   if (!opts) opts = {};
@@ -37,25 +38,6 @@ function isUndefinedOrNull(value) {
   return value === null || value === undefined;
 }
 
-var supportsArgumentsClass = (function(){
-  return Object.prototype.toString.call(arguments)
-}) == '[object Arguments]';
-
-if(supportsArgumentsClass) {
-  var isArguments = function(object) {
-    return Object.prototype.toString.call(object) == '[object Arguments]';
-  }
-} else {
-  var isArguments = function(object){
-    return object &&
-      typeof object == 'object' &&
-      typeof object.length == 'number' &&
-      Object.prototype.hasOwnProperty.call(object, 'callee') &&
-      !Object.prototype.propertyIsEnumerable.call(object, 'callee') ||
-      false;
-  }
-}
-
 function objEquiv(a, b, opts) {
   if (!opts) opts = {};
   if (isUndefinedOrNull(a) || isUndefinedOrNull(b))

lib/is_arguments.js

@@ -0,0 +1,20 @@
+var supportsArgumentsClass = (function(){
+  return Object.prototype.toString.call(arguments)
+})() == '[object Arguments]';
+
+exports = module.exports = supportsArgumentsClass ? supported : unsupported;
+
+exports.supported = supported;
+function supported(object) {
+  return Object.prototype.toString.call(object) == '[object Arguments]';
+};
+
+exports.unsupported = unsupported;
+function unsupported(object){
+  return object &&
+    typeof object == 'object' &&
+    typeof object.length == 'number' &&
+    Object.prototype.hasOwnProperty.call(object, 'callee') &&
+    !Object.prototype.propertyIsEnumerable.call(object, 'callee') ||
+    false;
+};

test/cmp.js

@@ -1,5 +1,6 @@
 var test = require('tape');
 var equal = require('../');
+var isArguments = require('../lib/is_arguments.js');
 
 test('equal', function (t) {
     t.ok(equal(
@@ -54,6 +55,16 @@ test('arguments class', function (t) {
     t.end();
 });
 
+test('test the arguments shim', function (t) {
+    t.ok(isArguments.supported((function(){return arguments})()));
+    t.notOk(isArguments.supported([1,2,3]));
+
+    t.ok(isArguments.unsupported((function(){return arguments})()));
+    t.notOk(isArguments.unsupported([1,2,3]));
+
+    t.end();
+});
+
 test('dates', function (t) {
     var d0 = new Date(1387585278000);
     var d1 = new Date('Fri Dec 20 2013 16:21:18 GMT-0800 (PST)');