Ensure _.flattenDeep works on arrays with circular references. [closes #1664]

test/test.js

@@ -5081,6 +5081,32 @@
 
   /*--------------------------------------------------------------------------*/
 
+  QUnit.module('lodash.flattenDeep');
+
+  (function() {
+    QUnit.test('should flatten arrays with circular references', function(assert) {
+      assert.expect(2);
+
+      var array = [1, 2];
+      array.push(array);
+
+      var expected = [1, 2, 1, 2];
+
+      try {
+        var actual = _.flattenDeep(array);
+      } catch (e) {}
+
+      assert.deepEqual(actual, expected);
+
+      array = [1, 2];
+      array = [array, [array]];
+
+      assert.deepEqual(_.flattenDeep(array), expected);
+    });
+  }());
+
+  /*--------------------------------------------------------------------------*/
+
   QUnit.module('flatten methods');
 
   (function() {