'creating a user with a specific \'partner_id\' should not create a new partner'

def test_create_with_ancestor(self):

    partner_foo = self.env['res.partner'].create({'name': 'Foo'})
    partners_before = self.env['res.partner'].search([])
    user_foo = self.env['res.users'].create({'partner_id': partner_foo.id, 'login': 'foo'})
    partners_after = self.env['res.partner'].search([])
    self.assertEqual(partners_before, partners_after)
    self.assertEqual(user_foo.name, 'Foo')
    self.assertEqual(user_foo.partner_id, partner_foo)
