Add tests for managemails.models

This commit adds tests for managemails.models to improve the test
coverage of that model. There are some changes to the classes in
managemails.models too:

- add a method create_mailbox to MailboxManager
- properly handle uncommited mailaddresses in MailAddress.set_mailbox
  and MailAddress.set_forward_addresses

gnuviechadmin/managemails/models.py

@@ -85,6 +85,23 @@ class MailboxManager(models.Manager):
             active=True, osuser=osuser,
         )
 
+    def create_mailbox(self, osuser, password=None, commit=True):
+        """
+        Create a new mailbox for the given operating system user.
+
+        :param osuser: a :py:class:`osuser.models.OsUser` instance
+        :param password: an optional password
+        :param commit: whether the mailbox should be commited to the database
+        :return: mailbox instance
+        :rtype: :py:class:`managemails.models.Mailbox`
+
+        """
+        mailbox = self.create(
+            osuser=osuser, username=self.get_next_mailbox_name(osuser))
+        if password is not None:
+            mailbox.set_password(password)
+        return mailbox
+
 
 @python_2_unicode_compatible
 class Mailbox(ActivateAbleMixin, TimeStampedModel):
@@ -176,9 +193,12 @@ class MailAddress(ActivateAbleMixin, TimeStampedModel, models.Model):
             for mafwd in MailAddressForward.objects.filter(mailaddress=self):
                 mafwd.delete()
         else:
-            mabox = MailAddressMailbox(mailaddress=self, mailbox=mailbox)
             if commit:
+                self.save()
+                mabox = MailAddressMailbox(mailaddress=self, mailbox=mailbox)
                 mabox.save()
+            else:
+                mabox = MailAddressMailbox(mailaddress=self, mailbox=mailbox)
         return mabox
 
     def set_forward_addresses(self, addresses, commit=True):
@@ -211,6 +231,8 @@ class MailAddress(ActivateAbleMixin, TimeStampedModel, models.Model):
                         mafwd.save()
                     retval.append(mafwd)
         else:
+            if commit:
+                self.save()
             for target in addresses:
                 mafwd = MailAddressForward(mailaddress=self, target=target)
                 if commit: