Factory Boy for test data in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Factory Boy factory produce?

Given the following factory definition, what will be the value of user.email after user = UserFactory() is executed?

Django

import factory
from myapp.models import User

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = User

    username = factory.Sequence(lambda n: f'user{n}')
    email = factory.LazyAttribute(lambda obj: f'{obj.username}@example.com')

user = UserFactory()

A "[e-mail]"

B Raises an AttributeError

C "[e-mail]"

D "[e-mail]"

💡 Hint

Look at how the username is generated and how email uses it.

The username is generated using factory.Sequence starting at 0, so the first user has username user0. The email uses LazyAttribute to build the email from the username, so it becomes [e-mail].

📝 Syntax

intermediate

Which factory definition has a syntax error?

Identify the factory definition that will cause a syntax error when run.

A

class ProductFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Product
    price = factory.Faker('random_number', digits=3)

B

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tcudorP = ledom        
:ateM ssalc    
:)yrotcaFledoMognajD.ognajd.yrotcaf(yrotcaFtcudorP ssalc

C

class ProductFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Product
    name = factory.Faker('word')
    price = factory.Faker('random_number', digits=3)

D

class ProductFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Product
    name = factory.Faker('word')

💡 Hint

Check the commas between arguments in function calls.

Option A is missing a comma between the string and the keyword argument in factory.Faker('random_number' digits=3), causing a syntax error.

❓ state_output

advanced

What is the value of order.total after creation?

Given this factory and model, what will order.total be after order = OrderFactory()?

Django

import factory
from myapp.models import Order

class OrderFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Order

    quantity = 3
    price_per_item = 10
    total = factory.LazyAttribute(lambda o: o.quantity * o.price_per_item)

order = OrderFactory()

A 0

B None

C Raises AttributeError

D 30

💡 Hint

Look at how total is calculated using LazyAttribute.

The total field uses LazyAttribute to multiply quantity (3) by price_per_item (10), resulting in 30.

🔧 Debug

advanced

Why does this factory raise a RecursionError?

Examine the factory below. Why does creating an instance with profile = ProfileFactory() cause a RecursionError?

Django

import factory
from myapp.models import Profile, User

class UserFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = User

    username = factory.Sequence(lambda n: f'user{n}')

class ProfileFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Profile

    user = factory.SubFactory(UserFactory)
    friend = factory.SubFactory('myapp.factories.ProfileFactory')

profile = ProfileFactory()

A Because UserFactory is missing a required field

B Because factory.SubFactory requires a callable, not a string

C Because ProfileFactory references itself in friend causing infinite recursion

D Because Profile model does not have a friend field

💡 Hint

Look at the friend field in ProfileFactory.

The friend field uses SubFactory referencing ProfileFactory itself, causing infinite recursion when creating a profile.

🧠 Conceptual

expert

Which option correctly uses Factory Boy to create related objects with different attributes?

You want to create a Book with two Author objects, each having different names. Which factory setup achieves this correctly?

Django

from myapp.models import Book, Author
import factory

class AuthorFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Author

    name = factory.Sequence(lambda n: f'Author {n}')

class BookFactory(factory.django.DjangoModelFactory):
    class Meta:
        model = Book

    title = 'My Book'
    authors = factory.RelatedFactoryList(AuthorFactory, related_name='book', size=2)

A Use SubFactory twice in BookFactory for authors with fixed names

B Use RelatedFactoryList with size=2 and AuthorFactory with Sequence for names

C Use RelatedFactoryList with size=2 but AuthorFactory has fixed name 'Author'

D Use a post_generation hook to add two authors with different names manually

💡 Hint

Think about how to create multiple related objects with unique attributes.

Option B uses RelatedFactoryList with size=2 to create two authors. The Sequence in AuthorFactory ensures different names. This is the correct pattern.