Verify only array is passed to insert function

Throw TypeError if insert receives something other than an array

Author: acarrau

test/array.builders.js

@@ -209,6 +209,9 @@ $(document).ready(function() {
   });
 
   test('insert', function(){
+    var throwingFn = function() { _.insert({}, 0, 1); };
+    throws(throwingFn, TypeError, 'throws a TypeError when passing an object literal');
+    
     deepEqual(_.insert([], 0, 1), [1],'inserts item in empty array');
     deepEqual(_.insert([2], 0, 1), [1,2],'inserst item at the corret index');
     deepEqual(_.insert([1,2], 2, 3), [1,2,3],'inserts item at the end of array if exceeding index');

underscore.array.builders.js

@@ -202,6 +202,7 @@
     // Inserts an item in an array at the specific index mutating the original
     // array and returning it.
     insert: function(array, index, item){
+      if (!_.isArray(array)) throw new TypeError('Expected an array as the first argument');
       splice.call(array, index, 0, item);
       return array;
     }