Django REST Framework tests

models.py

from django.db import models


class Bike(models.Model):
    COLOR_OPTIONS = (('yellow', 'Yellow'), ('red', 'Red'), ('black', 'Black'))

    color = models.CharField(max_length=255, null=True, blank=True,
                             choices=COLOR_OPTIONS)
    size = models.DecimalField(max_digits=4, decimal_places=2, null=True, blank=True)

serializers.py

from rest_framework import serializers
from bikes.models import Bike


class BikeSerializer(serializers.ModelSerializer):
    COLOR_OPTIONS = ('yellow', 'black')

    color = serializers.ChoiceField(choices=COLOR_OPTIONS)
    size = serializers.FloatField(min_value=30.0, max_value=60.0)

    class Meta:
        model = Bike
        fields = ['color', 'size']

test_serializers.py

from decimal import Decimal
from rest_framework.test import APITestCase
from bikes.models import Bike
from bikes.serializers import BikeSerializer


class BikeSerializerTests(APITestCase):

    def setUp(self):
        self.bike_attributes = {
            'color': 'yellow',
            'size': Decimal('52.12')
        }

        self.serializer_data = {
            'color': 'black',
            'size': 51.23
        }

        self.bike = Bike.objects.create(**self.bike_attributes)
        self.serializer = BikeSerializer(instance=self.bike)

    def test_contains_expected_fields(self):
        data = self.serializer.data

        self.assertEqual(set(data.keys()), set(['color', 'size']))

    def test_color_field_content(self):
        data = self.serializer.data

        self.assertEqual(data['color'], self.bike_attributes['color'])

    def test_size_field_content(self):
        data = self.serializer.data

        self.assertEqual(data['size'], float(self.bike_attributes['size']))

    def test_size_lower_bound(self):
        self.serializer_data['size'] = 29.9

        serializer = BikeSerializer(data=self.serializer_data)

        self.assertFalse(serializer.is_valid())
        self.assertEqual(set(serializer.errors), set(['size']))

    def test_size_upper_bound(self):
        self.serializer_data['size'] = 60.1

        serializer = BikeSerializer(data=self.serializer_data)

        self.assertFalse(serializer.is_valid())
        self.assertEqual(set(serializer.errors), set(['size']))

    def test_float_data_correctly_saves_as_decimal(self):
        self.serializer_data['size'] = 31.789

        serializer = BikeSerializer(data=self.serializer_data)
        serializer.is_valid()

        new_bike = serializer.save()
        new_bike.refresh_from_db()

        self.assertEqual(new_bike.size, Decimal('31.79'))
        
    def test_color_must_be_in_choices(self):
        self.bike_attributes['color'] = 'red'

        serializer = BikeSerializer(instance=self.bike, data=self.bike_attributes)

        self.assertFalse(serializer.is_valid())
        self.assertEqual(set(serializer.errors.keys()), set(['color']))