'The system username is used if --username isn\'t provided.'

@mock.patch.object(changepassword.Command, '_get_pass', return_value='new_password')
def test_system_username(self, mock_get_pass):

    username = getpass.getuser()
    User.objects.create_user(username=username, password='qwerty')
    call_command('changepassword', stdout=self.stdout)
    self.assertIs(User.objects.get(username=username).check_password('new_password'), True)
