How to correct test for unicode strings with Django and Python 2

I need to test, whether the representation of my Django models are working with Unicode as it might be that users insert th9ings like ü or ¼ into it. To do so, I have this Django tests.py

# -*- coding: utf-8 -*-
from django.conf import settings
from django.contrib.auth.models import User
from django.core.urlresolvers import reverse
from django.test import TestCase
from django.utils import timezone

from .models import *
from .views import *

class CategoryTestCase(TestCase):
    """ Test to check whether category name is printed correctly.
        If there is a parent, it should be also printed seperated by a : """

    def setUp(self):
        self.cat1 = Category.objects.create(name=u'Category 1')
        self.cat2 = Category.objects.create(name=u'Category ü', parent=self.cat1)
        self.cat3 = Category.objects.create(name=u'Category 3', parent=self.cat2)

    def test_category_name(self):
        cat_result1 = u'Category 1'
        cat_result2 = u'Category 1' + settings.PARENT_DELIMITER + u'Category ü'
        cat_result3 = u'Category 1' + settings.PARENT_DELIMITER + u'Category ü' + settings.PARENT_DELIMITER + u'Category 3'
        self.assertEqual(self.cat1.__str__(), cat_result1)
        self.assertEqual(self.cat2.__str__(), cat_result2)
        self.assertEqual(self.cat3.__str__(), cat_result3)

This is intended to test this little model:

#...
from django.utils.encoding import python_2_unicode_compatible
#....
@python_2_unicode_compatible
class Category(models.Model):
    """ Representing a category a part might contains to.
    E.g. resistor """

    name = models.CharField(
        max_length=50,
        help_text=_("Name of the category.")
    )
    parent = models.ForeignKey(
        "self",
        null=True,
        blank=True,
        help_text=_("If having a subcateogry, the parent.")
    )
    description = models.TextField(
        _("Description"),
        blank=True,
        null=True,
        help_text=_("A chance to summarize usage of category.")
    )

    def __str__(self):
        if self.parent is None:
            return ('{}'.format(self.name))
        else:
            return ('%s%s%s' % (
                self.parent.__str__(),
                settings.PARENT_DELIMITER,
                self.name)
            )

    def get_parents(self):
        """ Returns a list with parants of that StoragePare incl itself"""
        result = []
        next = self
        while True:
            if next.id in result:
                raise(CircleDetectedException(
                    _('There seems to be a circle inside ancestors of %s.' % self.id)))
            else:
                result.append(next.id)
                if next.parent is not None:
                    next = next.parent
                else:
                    break
        return result

    def clean(self):
        pass

(stripped that a little)

When running this code via Python 3 and test or with Python2/3 executing as application it's working. Only the test with Python2 is failing so I assume it's something wrong with my idea how to test this. Based on the error message it appears that the Unicode string is somewhere not properly encoded and decoded.

======================================================================
FAIL: test_category_name (partsmanagement.tests.CategoryTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/frlan/quellen/partuniverse/partuniverse/partsmanagement/tests.py", line 31, in test_category_name
    self.assertEqual(self.cat2.__str__(), cat_result2)
AssertionError: 'Category 1->Category xc3xbc' != u'Category 1->Category xfc'

So my question is: How to do proper Unicode-representation testing with Django.