public function testValidateUrl()
 {
     $this->assertEquals('http://test.com', RestValidatorHelper::validate_url(['url' => 'http://test.com'], 'url'));
     TestHelper::assertException(function () {
         RestValidatorHelper::validate_url(['url' => 'FOO'], 'url');
     }, 'ValidationException');
     $this->assertEquals(null, RestValidatorHelper::validate_url([], 'url', ['required' => false]));
     TestHelper::assertException(function () {
         RestValidatorHelper::validate_url([], 'url');
     }, 'ValidationException');
 }