Celery/Django: Test if task ETA is set correctly in relation to datetime

I have a django model that stores a datetime, and I need to create a celery task that runs X days before this datetime, and one that runs at (or slightly after) this datetime.

How would I go about creating a unit test that checks whether the tasks ETA is set correctly in relation to the datetime?

I'm using Django 1.8, Celery and RabbitMQ