diff --git a/golem_resource_account/models/golem_resource_reservation.py b/golem_resource_account/models/golem_resource_reservation.py
index 9681a7e..582dd55 100644
--- a/golem_resource_account/models/golem_resource_reservation.py
+++ b/golem_resource_account/models/golem_resource_reservation.py
@@ -69,11 +69,24 @@ class GolemResourceReservation(models.Model):
     def create_invoice(self):
         """ Create invoice """
         for reservation in self:
+            if reservation.state != "validated":
+                raise UserError(
+                    _("The reservation '%s' is not validated, please validate it before \
+                      creating invoice") % reservation.name)
+
             inv_obj = self.env['account.invoice']
             partner_id = reservation.partner_id
             product = reservation.resource_id.product_tmpl_id
             amount = product.standard_price
-            quantity = reservation.hour_stop - reservation.hour_start
+            delta = fields.Datetime.from_string(reservation.date_stop) - \
+            fields.Datetime.from_string(reservation.date_start)
+
+            quantity = (delta.days * 24) + (delta.seconds/3600.0)
+            account_id = False
+            if not product:
+                raise UserError(
+                    _("There is no product linked to resource : '%s', you can't invoice \
+                      reservation with no product linked") % (reservation.resource_id.name,))
             if product.id:
                 account_id = product.property_account_income_id.id
 
diff --git a/golem_resource_account/tests/__init__.py b/golem_resource_account/tests/__init__.py
index 7d004f8..59f0980 100644
--- a/golem_resource_account/tests/__init__.py
+++ b/golem_resource_account/tests/__init__.py
@@ -15,3 +15,4 @@
 #
 #    You should have received a copy of the GNU Affero General Public License
 #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+from . import test_golem_reservation_invoice
diff --git a/golem_resource_account/tests/test_golem_reservation_invoice.py b/golem_resource_account/tests/test_golem_reservation_invoice.py
new file mode 100644
index 0000000..9af9dbd
--- /dev/null
+++ b/golem_resource_account/tests/test_golem_reservation_invoice.py
@@ -0,0 +1,102 @@
+# -*- coding: utf-8 -*-
+
+#    Copyright 2018 Youssef El Ouahby <youssef@yaltik.com>
+#    Copyright 2018 Fabien Bourgeois <fabien@yaltik.com>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU Affero General Public License as
+#    published by the Free Software Foundation, either version 3 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 Affero General Public License for more details.
+#
+#    You should have received a copy of the GNU Affero General Public License
+#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+""" GOLEM Resource Reservation testing """
+
+import logging
+from odoo.tests.common import TransactionCase
+from odoo.exceptions import ValidationError, UserError
+_LOGGER = logging.getLogger(__name__)
+
+
+class TestGolemResourceReservation(TransactionCase):
+    """ GOLEM Resource Reservation testing """
+
+    def setUp(self, *args, **kwargs):
+        """ Bootstrap Resource Reservation """
+        super(TestGolemResourceReservation, self).setUp(*args, **kwargs)
+        self.resource = self.env['golem.resource'].create({
+            'name': 'Resource',
+            'avaibility_start': '2018-01-01',
+            'avaibility_stop': '2020-01-01'
+        })
+        self.resource_val = self.env['golem.resource'].create({
+            'name': 'Resource to validate',
+            'avaibility_start': '2018-01-01',
+            'avaibility_stop': '2020-01-01',
+            'validation_required': True
+        })
+
+        self.timetable_obj = self.env['golem.resource.timetable']
+
+        timetable_data = {'resource_id': self.resource.id, 'weekday': '0',
+                          'time_start': 8.0, 'time_stop': 12.0}
+        timetable_data2 = {'resource_id': self.resource.id, 'weekday': '1',
+                           'availibility_24': True}
+        timetable_data3 = {'resource_id': self.resource.id, 'weekday': '2',
+                           'time_start': 7.0, 'time_stop': 23.98}
+        timetable_data4 = {'resource_id': self.resource.id, 'weekday': '3',
+                           'availibility_24': True}
+
+        self.timetable_obj.create(timetable_data)
+        self.timetable_obj.create(timetable_data2)
+        self.timetable_obj.create(timetable_data3)
+        self.timetable_obj.create(timetable_data4)
+
+        timetable_data['resource_id'] = self.resource_val.id
+        self.timetable_obj.create(timetable_data)
+
+        self.partner = self.env['res.partner'].create({'firstname': 'John',
+                                                       'lastname': 'DOE',
+                                                       'is_company': False})
+
+        self.data = {
+            'resource_id': self.resource.id,
+            'date_start': '2018-02-05 11:00:00', # is monday
+            'date_stop': '2018-02-05 12:00:00',
+            'partner_id': self.partner.id
+        }
+        self.res_obj = self.env['golem.resource.reservation']
+
+
+    def test_reservation_invoice_single(self):
+        """ Test reservation bases """
+        reservation = self.res_obj.create(self.data)
+        self.assertEqual(reservation.state, 'draft')
+        self.assertFalse(reservation.invoice_id)
+        #try to create invoice withoud validating reservation
+        with self.assertRaises(UserError) as err:
+            reservation.create_invoice()
+        self.assertIn(u'is not validated, please validate it', err.exception.args[0])
+        reservation.state_confirm()
+
+        #try to create invoice with no product linked
+        with self.assertRaises(UserError) as err:
+            reservation.create_invoice()
+        self.assertIn(u'no product linked to resource', err.exception.args[0])
+
+        reservation.resource_id.write({
+            'product_tmpl_id': self.env.ref('product.product_product_5').id})
+        reservation.create_invoice()
+        self.assertTrue(reservation.invoice_id)
+        self.assertEqual(reservation.invoicing_state,"draft")
+
+        """
+            self.assertEqual(reservation.state, 'validated')
+            reservation.create_invoice()
+            self.assertTrue(reservation.invoice_id)"""