models.py

from django.db import models


class Car(models.Model):
    AT = 'AT'
    MA = 'MA'
    CAMBIO = [
        (AT, 'Automatic'),
        (MA, 'Manual')
    ]
    name = models.CharField(
        verbose_name='Nome',
        max_length=50
    )
    price = models.DecimalField(
        'Preço',
        decimal_places=2,
        max_digits=5
    )
    year = models.SmallIntegerField(
        'Ano'
    )
    transmission = models.CharField(
        'Transmissão',
        max_length=2,
        choices=CAMBIO,
        default=MA,
    )
    manufacturer = models.ForeignKey(
        'Manufacturer',
        verbose_name='Fabricante',
        on_delete=models.CASCADE,
        related_name='cars'
    )

    def __str__(self):
        return f'{self.name} - {self.manufacturer}'

    class Meta:
        verbose_name = 'Carro'
        verbose_name_plural = 'Carros'
        ordering = ['name']


class Manufacturer(models.Model):
    name = models.CharField(
        'nome',
        max_length=20
    )

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = 'Fabricante'
        verbose_name_plural = 'Fabricantes'


class City(models.Model):
    name = models.CharField(
        'Nome',
        max_length=50
    )
    state = models.ManyToManyField(
        'State',
        verbose_name='Estado'
    )

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = 'Cidade'
        verbose_name_plural = 'Cidades'


class State(models.Model):
    SP = 'sp'
    RJ = 'rj'
    STATE = [
        (SP, 'São Paulo'),
        (RJ, 'Rio de Janeiro'),
    ]
    name = models.CharField(
        'Nome',
        max_length=2,
        choices=STATE,
        default=SP
    )

    def __str__(self):
        return self.name

    class Meta:
        verbose_name = 'Estado'
        verbose_name_plural = 'Estados'

stack_trace

Operations to perform:
  Synchronize unmigrated apps: debug_toolbar, django_extensions, messages, staticfiles
  Apply all migrations: admin, auth, contenttypes, core, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying admin.0002_logentry_remove_auto_add... OK
  Applying admin.0003_logentry_add_action_flag_choices... OK
  Applying contenttypes.0002_remove_content_type_name... OK
  Applying auth.0002_alter_permission_name_max_length... OK
  Applying auth.0003_alter_user_email_max_length... OK
  Applying auth.0004_alter_user_username_opts... OK
  Applying auth.0005_alter_user_last_login_null... OK
  Applying auth.0006_require_contenttypes_0002... OK
  Applying auth.0007_alter_validators_add_error_messages... OK
  Applying auth.0008_alter_user_username_max_length... OK
  Applying auth.0009_alter_user_last_name_max_length... OK
  Applying auth.0010_alter_group_name_max_length... OK
  Applying auth.0011_update_proxy_permissions... OK
  Applying auth.0012_alter_user_first_name_max_length... OK
  Applying core.0001_initial... OK
  Applying core.0002_alter_car_manufacturer_alter_city_state... OK
  Applying sessions.0001_initial... OK
Creating test database for alias 'default' ('file:memorydb_default?mode=memory&cache=shared')...
FAILED                                          [100%]
core\tests\test_models.py:34 (test_car)
'' != 'Doblô'

Expected :'Doblô'
Actual   :''
<Click to see difference>

car = <Car:  - FIAT>

    def test_car(car):
>       assert car.name == 'Doblô'
E       AssertionError: assert '' == 'Doblô'
E         - Doblô

test_models.py:36: AssertionError