Google\Cloud\Logging\PsrLogger::validateLogLevel PHP Method

    private function validateLogLevel($level)
    {
        $map = $this->logger->getLogLevelMap();
        $level = (string) $level;
        if (isset($map[$level]) || isset(array_flip($map)[strtoupper($level)])) {
            return true;
        }
        throw new InvalidArgumentException("Severity level '{$level}' is not defined.");
    }