You are currently reading the documentation for v6, while the latest version is v8.

Testing an automation mail

Before sending an automation mail, you can send a test to a given email address.

// to a single email address

// to multiple email addresses at once
$automationMail->sentTestMail(['', ''])

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.