library/library_checkout/tests/__init__.py

from . import test_checkout_mass_message

from odoo.tests.common import TransactionCase

class TestWizard(TransactionCase):
    def setUp(self, *args, **kwargs):
        super(TestWizard, self).setUp(*args, **kwargs)
        # Add test setup code here...

    def test_button_send(self):
        """Send button should create messages on Checkouts"""
        # Add test code