private function assertConfigIsValid($config)
 {
     if (!is_array($config)) {
         throw InvalidConfigException::fromPHPFileError($this->filename);
     }
 }
 public function testItCanBeCreatedFromTheFileName()
 {
     assertSame('"example.cfg" does not return a PHP array.', InvalidConfigException::fromPHPFileError('example.cfg')->getMessage());
 }