Testing Django and model methods

I wondering what is the best practice to write code for good testing. E.g.

class Visits(models.Model):
    user = models.ForeignKey(User)
    visited_at = models.DateTimeField()

    def __unicode__(self):
        return "{}-{}".format(self.user, self.visited_at)

And I need a function wich get me only visits for current user from last day. What should I do? Make view for this and test it? Or make model methods? What is the best to test?