public function testValidateCountryCode()
 {
     $this->assertEquals('US', RestValidatorHelper::validate_country_code(['cc' => 'US'], 'cc'));
     $this->assertEquals(null, RestValidatorHelper::validate_country_code([], 'cc', ['required' => false]));
     TestHelper::assertException(function () {
         RestValidatorHelper::validate_country_code(['cc' => 'FOO'], 'cc');
     }, 'ValidationException');
     TestHelper::assertException(function () {
         RestValidatorHelper::validate_country_code([], 'cc');
     }, 'ValidationException');
 }