test for CursorPagination with floating point field

fpcursorpagination.py

class FloatingPointCursorPagination(CursorPagination):
    __rounding_down = decimal.Context(prec=14, rounding=decimal.ROUND_FLOOR)
    __rounding_up = decimal.Context(prec=14, rounding=decimal.ROUND_CEILING)

    def _get_position_from_instance(self, instance, ordering):
        field_name = ordering[0].lstrip('-')
        if isinstance(instance, dict):
            attr = instance[field_name]
        else:
            attr = getattr(instance, field_name)

        if isinstance(attr, float):
            # repr gives more precision than str
            # but we still lost some precision just from the postgresql-to-python translation.
            if ordering[0][0] == '-':
                attr = self.__rounding_down.create_decimal_from_float(attr)
            else:
                attr = self.__rounding_up.create_decimal_from_float(attr)

        attr_str = force_text(attr)
        return attr_str

test_cursorpagination.py

from django.db import models
from rest_framework import viewsets
from rest_framework.pagination import CursorPagination


class FloatyModel(models.Model):
    score = models.FloatField()


class FloatyViewSet(viewsets.ReadOnlyModelViewSet):
    queryset = FloatyModel.objects.all().order_by('-score')
    pagination_class = CursorPagination
    page_size = 3


class TestFloatingPointCursorPagination(APITestCase):
    def test_page_boundary_does_not_repeat_elements(self, test_data):
        for i in range(12):
            FloatyModel.objects.create(score=i/9.0)

        viewset_url = 'FIXME'
        first_response = self.client.get(viewset_url)

        first_page_last_item = first_response.data['results'][-1]

        second_response = self.client.get(first_response['next'])

        second_page_first_item = second_response.data['results'][0]

        self.assertNotEqual(first_page_last_item['pk'], second_page_first_item['pk'])
        self.assertGreater(first_page_last_item['score'], second_page_first_item['score'])