diff --git a/cotisations/migrations/0041_auto_20191103_2131.py b/cotisations/migrations/0041_auto_20191103_2131.py
new file mode 100644
index 00000000..09f763ed
--- /dev/null
+++ b/cotisations/migrations/0041_auto_20191103_2131.py
@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.23 on 2019-11-03 20:31
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('cotisations', '0040_auto_20191002_2335'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='balancepayment',
+            name='payment',
+            field=models.OneToOneField(editable=False, on_delete=django.db.models.deletion.CASCADE, related_name='payment_method_balance', to='cotisations.Paiement'),
+        ),
+        migrations.AlterField(
+            model_name='chequepayment',
+            name='payment',
+            field=models.OneToOneField(editable=False, on_delete=django.db.models.deletion.CASCADE, related_name='payment_method_cheque', to='cotisations.Paiement'),
+        ),
+        migrations.AlterField(
+            model_name='comnpaypayment',
+            name='payment',
+            field=models.OneToOneField(editable=False, on_delete=django.db.models.deletion.CASCADE, related_name='payment_method_comnpay', to='cotisations.Paiement'),
+        ),
+        migrations.AlterField(
+            model_name='freepayment',
+            name='payment',
+            field=models.OneToOneField(editable=False, on_delete=django.db.models.deletion.CASCADE, related_name='payment_method_free', to='cotisations.Paiement'),
+        ),
+        migrations.AlterField(
+            model_name='notepayment',
+            name='payment',
+            field=models.OneToOneField(editable=False, on_delete=django.db.models.deletion.CASCADE, related_name='payment_method_note', to='cotisations.Paiement'),
+        ),
+    ]
diff --git a/cotisations/payment_methods/balance/models.py b/cotisations/payment_methods/balance/models.py
index 221cca3e..e3e05ea4 100644
--- a/cotisations/payment_methods/balance/models.py
+++ b/cotisations/payment_methods/balance/models.py
@@ -40,7 +40,7 @@ class BalancePayment(PaymentMethodMixin, models.Model):
     payment = models.OneToOneField(
         Paiement,
         on_delete=models.CASCADE,
-        related_name='payment_method',
+        related_name='payment_method_balance',
         editable=False
     )
     minimum_balance = models.DecimalField(
diff --git a/cotisations/payment_methods/cheque/models.py b/cotisations/payment_methods/cheque/models.py
index 8f00ff46..a834bb93 100644
--- a/cotisations/payment_methods/cheque/models.py
+++ b/cotisations/payment_methods/cheque/models.py
@@ -38,7 +38,7 @@ class ChequePayment(PaymentMethodMixin, models.Model):
     payment = models.OneToOneField(
         Paiement,
         on_delete=models.CASCADE,
-        related_name='payment_method',
+        related_name='payment_method_cheque',
         editable=False
     )
 
diff --git a/cotisations/payment_methods/comnpay/models.py b/cotisations/payment_methods/comnpay/models.py
index 7fac089a..a5568f22 100644
--- a/cotisations/payment_methods/comnpay/models.py
+++ b/cotisations/payment_methods/comnpay/models.py
@@ -41,7 +41,7 @@ class ComnpayPayment(PaymentMethodMixin, models.Model):
     payment = models.OneToOneField(
         Paiement,
         on_delete=models.CASCADE,
-        related_name='payment_method',
+        related_name='payment_method_comnpay',
         editable=False
     )
     payment_credential = models.CharField(
diff --git a/cotisations/payment_methods/free/models.py b/cotisations/payment_methods/free/models.py
index 46ecca87..2931faad 100644
--- a/cotisations/payment_methods/free/models.py
+++ b/cotisations/payment_methods/free/models.py
@@ -38,7 +38,7 @@ class FreePayment(PaymentMethodMixin, models.Model):
     payment = models.OneToOneField(
         Paiement,
         on_delete=models.CASCADE,
-        related_name='payment_method',
+        related_name='payment_method_free',
         editable=False
     )
 
diff --git a/cotisations/payment_methods/note_kfet/models.py b/cotisations/payment_methods/note_kfet/models.py
index be54bd54..0e2ebea1 100644
--- a/cotisations/payment_methods/note_kfet/models.py
+++ b/cotisations/payment_methods/note_kfet/models.py
@@ -42,7 +42,7 @@ class NotePayment(PaymentMethodMixin, models.Model):
     payment = models.OneToOneField(
         Paiement,
         on_delete = models.CASCADE,
-        related_name = 'payment_method',
+        related_name = 'payment_method_note',
         editable = False
     )
     server = models.CharField(
diff --git a/cotisations/test_models.py b/cotisations/test_models.py
new file mode 100644
index 00000000..33f32a18
--- /dev/null
+++ b/cotisations/test_models.py
@@ -0,0 +1,49 @@
+from django.test import TestCase
+
+import datetime
+from django.utils import timezone
+
+from users.models import User
+from .models import Vente, Facture, Cotisation, Paiement
+
+class VenteModelTests(TestCase):
+    def setUp(self):
+        self.user = User.objects.create(
+            pseudo="testUser",
+            email="test@example.org"
+        )
+        self.paiement = Paiement.objects.create(
+            moyen="test payment"
+        )
+        self.f = Facture.objects.create(
+            user=self.user,
+            paiement=self.paiement,
+            valid=True
+        )
+
+    def test_one_day_cotisation(self):
+        """
+        It should be possible to have one day membership.
+        """
+        date = timezone.now()
+        purchase = Vente.objects.create(
+            facture=self.f,
+            number=1,
+            name="Test purchase",
+            duration=0,
+            duration_days=1,
+            type_cotisation="All",
+            prix=0,
+        )
+        self.assertAlmostEqual(
+            self.user.end_connexion() - date,
+            datetime.timedelta(days=1),
+            delta=datetime.timedelta(seconds=1)
+        )
+
+    def tearDown(self):
+        self.f.delete()
+        self.user.delete()
+        self.paiement.delete()
+
+
diff --git a/cotisations/tests.py b/cotisations/tests.py
deleted file mode 100644
index b2ecee78..00000000
--- a/cotisations/tests.py
+++ /dev/null
@@ -1,28 +0,0 @@
-# Re2o est un logiciel d'administration développé initiallement au rezometz. Il
-# se veut agnostique au réseau considéré, de manière à être installable en
-# quelques clics.
-#
-# Copyright © 2017  Gabriel Détraz
-# Copyright © 2017  Lara Kermarec
-# Copyright © 2017  Augustin Lemesle
-#
-# This program is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 2 of the License, or
-# (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License along
-# with this program; if not, write to the Free Software Foundation, Inc.,
-# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
-"""cotisations.tests
-The tests for the Cotisations module.
-"""
-
-# from django.test import TestCase
-
-# Create your tests here.