Zend_Mail error at php unit testing

A particular code makes the error

include_once "Zend/Mail.php";
$mail->setReplyTo($this->smtp_from,开发者_StackOverflow'comp');

The error is: PHP Fatal error: Call to undefined method Zend_Mail::setReplyTo()

Can you point out possible causes of this?

There was a bug in older versions about that method, for safety use this instead:

$mail->addHeader('Reply-To', $this->smtp_from);