Before sending an automation mail, you can send a test to a given email address.
// to a single email address
$automationMail->sendTestMail('john@example.com');
// to multiple email addresses at once
$automationMail->sentTestMail(['john@example.com', 'paul@example.com'])
In the sent mail the placeholders won't be replaced. Rest assured that when you send the mail to your subscribers, they will be replaced.