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

Testing a campaign

Before sending a campaign to an entire list, you can send a test to a given email address.

// to a single email address

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

In the sent mail the placeholders won’t be replaced. Rest assured that when you send the mail to your entire list, they will be replaced.

Creating a campaign