addTag() public method

Note that third-party libraries might also tag your session. Therefore it is recommended to use namespaced tags such as "Acme-Demo-MySpecialTag".
public addTag ( string $tag ) : void
$tag string The tag – must match be a valid cache frontend tag
return void
 /**
  * @test
  * @expectedException \Neos\Flow\Session\Exception\SessionNotStartedException
  */
 public function addTagThrowsExceptionIfCalledOnNonStartedSession()
 {
     $session = new Session();
     $session->addTag('MyTag');
 }