I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework.

Now some people argue that if a library is stable enough and won't change often then there is no need to wrap it. So assuming that Zend_Mail is stable and won't change and it fits my needs entirely, then I won't need a wrapper for it.

Now take a look at my class Logger that depends on Zend_Mail:

class Logger{
    private $mailer;    
    function __construct(Zend_Mail $mail){
        $this->mail=$mail;
    }    
   function toBeTestedFunction(){
      //Some code
      $this->mail->setTo('some value');
      $this->mail->setSubject('some value');
      $this->mail->setBody('some value');
      $this->mail->send();
     //Some
   }        
}

However, Unit testing demands that I test one component at a time, so I need to mock the Zend_Mail class. In addition I'm violating the Dependency Inversion principle as my Logger class now depends on concretion not abstraction.

Now is wrapping Zend_Mail the only solution or is there a better approach to this problem?

The code is in PHP, but answers doesn't have to be. This is more of a design issue than a language specific feature