[Robustness] use cached .test

lib/test.js

@@ -654,7 +654,7 @@ Test.prototype['throws'] = function (fn, expected, msg, extra) {
                 passed = expected.call({}, caught.error) === true;
             }
         } else if (isRegExp(expected)) {
-            passed = expected.test(caught.error);
+            passed = $test(expected, caught.error);
             expected = inspect(expected);
         } else if (expected && typeof expected === 'object') { // Handle validation objects.
             var keys = objectKeys(expected);