factory_boy integration with the pytest runner

pytest-factoryboy makes it easy to combine factory approach to the test setup with the dependency injection, heart of the pytest fixtures.

Install pytest-factoryboy

pip install pytest-factoryboy

Concept

Library exports a function to register factories as fixtures. Fixtures are contributed to the same module where register function is called.

Model Fixture

Model fixture implements an instance of a model created by the factory. Name convention is model's lowercase-underscore class name.

import factory
from pytest_factoryboy import register

@register
class AuthorFactory(factory.Factory):
    class Meta:
        model = Author

    name = "Charles Dickens"


def test_model_fixture(author):
    assert author.name == "Charles Dickens"

Attributes are Fixtures

There are fixtures created automatically for factory attributes. Attribute names are prefixed with the model fixture name and double underscore (similar to the convention used by factory_boy).

@pytest.mark.parametrize("author__name", ["Bill Gates"])
def test_model_fixture(author):
    assert author.name == "Bill Gates"

Multiple fixtures

Model fixtures can be registered with specific names. For example, if you address instances of some collection by the name like "first", "second" or of another parent as "other":

register(AuthorFactory)  # author
register(AuthorFactory, "second_author")  # second_author


@register  # book
@register(_name="second_book")  # second_book
@register(_name="other_book")  # other_book, book of another author
class BookFactory(factory.Factory):
    class Meta:
        model = Book


@pytest.fixture
def other_book__author(second_author):
    """Make the relation of the `other_book.author` to `second_author`."""
    return second_author


def test_book_authors(book, second_book, other_book, author, second_author):
    assert book.author == second_book.author == author
    assert other_book.author == second_author

SubFactory

Sub-factory attribute points to the model fixture of the sub-factory. Attributes of sub-factories are injected as dependencies to the model fixture and can be overridden via the parametrization.

Related Factory

Related factory attribute points to the model fixture of the related factory. Attributes of related factories are injected as dependencies to the model fixture and can be overridden via the parametrization.

post-generation

Post-generation attribute fixture implements only the extracted value for the post generation function.

Factory Fixture

pytest-factoryboy also registers factory fixtures, to allow their use without importing them. The fixture name convention is to use the lowercase-underscore form of the class name.

import factory
from pytest_factoryboy import register

class AuthorFactory(factory.Factory):
    class Meta:
        model = Author


register(AuthorFactory)  # => author_factory


def test_factory_fixture(author_factory):
    author = author_factory(name="Charles Dickens")
    assert author.name == "Charles Dickens"

Integration

An example of factory_boy and pytest integration.

# tests/factories.py

import factory
from app import models
from faker import Factory as FakerFactory

faker = FakerFactory.create()


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

    name = factory.LazyFunction(lambda: faker.name())


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

    title = factory.LazyFunction(lambda: faker.sentence(nb_words=4))
    author = factory.SubFactory(AuthorFactory)

# tests/conftest.py

from pytest_factoryboy import register

from . import factories

register(factories.AuthorFactory)
register(factories.BookFactory)

# tests/test_models.py

from app.models import Book
from .factories import BookFactory


def test_book_factory(book_factory):
    """Factories become fixtures automatically."""
    assert book_factory is BookFactory


def test_book(book):
    """Instances become fixtures automatically."""
    assert isinstance(book, Book)


@pytest.mark.parametrize("book__title", ["PyTest for Dummies"])
@pytest.mark.parametrize("author__name", ["Bill Gates"])
def test_parametrized(book):
    """You can set any factory attribute as a fixture using naming convention."""
    assert book.title == "PyTest for Dummies"
    assert book.author.name == "Bill Gates"

Fixture partial specialization

There is a possibility to pass keyword parameters in order to override factory attribute values during fixture registration. This comes in handy when your test case is requesting a lot of fixture flavors. Too much for the regular pytest parametrization. In this case, you can register fixture flavors in the local test module and specify value deviations inside register function calls.

register(AuthorFactory, "male_author", gender="M", name="John Doe")
register(AuthorFactory, "female_author", gender="F")


@pytest.fixture
def female_author__name():
    """Override female author name as a separate fixture."""
    return "Jane Doe"


@pytest.mark.parametrize("male_author__age", [42])  # Override even more
def test_partial(male_author, female_author):
    """Test fixture partial specialization."""
    assert male_author.gender == "M"
    assert male_author.name == "John Doe"
    assert male_author.age == 42

    assert female_author.gender == "F"
    assert female_author.name == "Jane Doe"

Fixture attributes

Sometimes it is necessary to pass an instance of another fixture as an attribute value to the factory. It is possible to override the generated attribute fixture where desired values can be requested as fixture dependencies. There is also a lazy wrapper for the fixture that can be used in the parametrization without defining fixtures in a module.

LazyFixture constructor accepts either existing fixture name or callable with dependencies:

import pytest
from pytest_factoryboy import register, LazyFixture


@pytest.mark.parametrize("book__author", [LazyFixture("another_author")])
def test_lazy_fixture_name(book, another_author):
    """Test that book author is replaced with another author by fixture name."""
    assert book.author == another_author


@pytest.mark.parametrize("book__author", [LazyFixture(lambda another_author: another_author)])
def test_lazy_fixture_callable(book, another_author):
    """Test that book author is replaced with another author by callable."""
    assert book.author == another_author


# Can also be used in the partial specialization during the registration.
register(BookFactory, "another_book", author=LazyFixture("another_author"))

Generic container classes as models

It's often useful to create factories for dict or other common generic container classes. In that case, you should wrap the container class around named_model(...), so that pytest-factoryboy can correctly determine the model name when using it in a SubFactory or RelatedFactory.

Pytest-factoryboy will otherwise raise a warning.

For example:

import factory
from pytest_factoryboy import named_model, register

@register
class JSONPayload(factory.Factory):
    class Meta:
        model = named_model("JSONPayload", dict)

    name = "foo"


def test_foo(json_payload):
    assert json_payload.name == "foo"

As a bonus, factory is automatically registering the json_payload fixture (rather than dict), so there is no need to override @register(_name="json_payload")).

Post-generation dependencies

Unlike factory_boy which binds related objects using an internal container to store results of lazy evaluations, pytest-factoryboy relies on the PyTest request.

Circular dependencies between objects can be resolved using post-generation hooks/related factories in combination with passing the SelfAttribute, but in the case of PyTest request fixture functions have to return values in order to be cached in the request and to become available to other fixtures.

That's why evaluation of the post-generation declaration in pytest-factoryboy is deferred until calling the test function. This solves circular dependency resolution for situations like:

o->[ A ]-->[ B ]<--[ C ]-o
|                        |
o----(C depends on A)----o

On the other hand, deferring the evaluation of post-generation declarations evaluation makes their result unavailable during the generation of objects that are not in the circular dependency, but they rely on the post-generation action.

pytest-factoryboy is trying to detect cycles and resolve post-generation dependencies automatically.

from pytest_factoryboy import register


class Foo(object):
    def __init__(self, value):
        self.value = value


class Bar(object):
    def __init__(self, foo):
        self.foo = foo


@register
class FooFactory(factory.Factory):
    class Meta:
        model = Foo

    value = 0

    @factory.post_generation
    def set1(foo, create, value, **kwargs):
        foo.value = 1

@register
class BarFactory(factory.Factory):
    class Meta:
        model = Bar

    foo = factory.SubFactory(FooFactory)

    @classmethod
    def _create(cls, model_class, foo):
        assert foo.value == 1  # Assert that set1 is evaluated before object generation
        return super(BarFactory, cls)._create(model_class, foo=foo)


# Forces 'set1' to be evaluated first.
def test_depends_on_set1(bar):
    """Test that post-generation hooks are done and the value is 2."""
    assert bar.foo.value == 1

Hooks

pytest-factoryboy exposes several pytest hooks which might be helpful for e.g. controlling database transaction, for reporting etc:

• pytest_factoryboy_done(request) - Called after all factory-based fixtures and their post-generation actions have been evaluated.

License

This software is licensed under the MIT license.

© 2015 Oleg Pidsadnyi, Anatoly Bubenkov and others