Fix tests

apps/registration/models.py

@@ -340,6 +340,9 @@ class Payment(models.Model):
     def get_absolute_url(self):
         return reverse_lazy("registration:user_detail", args=(self.registration.user.id,))
 
+    def __str__(self):
+        return _("Payment of {registration}").format(registration=self.registration)
+
     class Meta:
         verbose_name = _("payment")
         verbose_name_plural = _("payments")

apps/registration/signals.py

@@ -3,7 +3,6 @@
 
 from django.contrib.auth.models import User
 from tfjm.lists import get_sympa_client
-from tfjm.matrix import Matrix
 
 from .models import AdminRegistration, Payment, Registration