WordPress at a glance
function is not described

PHPMailer\PHPMailer

SMTP::noop() public WP 1.0

Send an SMTP NOOP command. Used to keep keep-alives alive, doesn't actually do anything.

{} It's a method of the class: SMTP{}

No Hooks.

Return

true|false. Nothing.

Usage

$SMTP = new SMTP();
$SMTP->noop();

Code of SMTP::noop() WP 5.7.2

<?php
public function noop()
{
    return $this->sendCommand('NOOP', 'NOOP', 250);
}