Unit tests + minor bugfix

- added unit tests for new methods in Models\Subscriber
- removed check for "isNew()". It was an unecessary check. Also isNew() always returns false once the new model is saved.

lib/Models/Subscriber.php

@@ -70,11 +70,8 @@ class Subscriber extends Model {
       } else {
         // reset status of existing subscribers if signup confirmation
         // is turned on
-        if($subscriber->isNew() === false) {
-          // existing subscriber
-          if($subscriber->status !== 'subscribed') {
-            $subscriber->set('status', 'unconfirmed');
-          }
+        if($subscriber->status !== 'subscribed') {
+          $subscriber->set('status', 'unconfirmed');
         }
 
         // send confirmation email to unconfirmed subscribers