Add python test case

Hello,

Add a python test case in website_forum module.

More details:
Task link :- https://www.odoo.com/web#id=8745&view_type=form&model=project.task&menu_id=3942&action=327
Pad link :- https://pad.odoo.com/p/r.EsLOcZQQuvZYB4ll

Thanks,
ssh-odoo
and maybe use `self.env` to write the test using the new API?