Add more tests for basket subscription.
Add more tests for basket subscription.

* Small changes in test_tasks.

johngian/mozillians,fxa90id/mozillians,akatsoulas/mozillians,fxa90id/mozillians,fxa90id/mozillians,akatsoulas/mozillians,mozilla/mozillians,mozilla/mozillians,akatsoulas/mozillians,mozilla/mozillians,akatsoulas/mozillians,johngian/mozillians,johngian/mozillians,fxa90id/mozillians,johngian/mozillians,mozilla/mozillians