factory_boy

factory_boy is a fixtures replacement based on thoughtbot's factory_girl . Like factory_girl it has a straightforward definition syntax, support for multiple build strategies (saved instances, unsaved instances, attribute dicts, and stubbed objects), and support for multiple factories for the same class, including factory inheritance. Django support is included, and support for other ORMs can be easily added.

Credits

This README parallels the factory_girl README as much as possible; text and examples are reproduced for comparison purposes. Ruby users of factory_girl should feel right at home with factory_boy in Python.

factory_boy was written by Mark Sandstrom.

Thank you Joe Ferris and thoughtbot for creating factory_girl.

Download

Github: http://github.com/dnerdy/factory_boy/tree/master

easy_install:

easy_install factory_boy

Source:

# Download the source and run
python setup.py install

Defining factories

Factories declare a set of attributes used to instantiate an object. The name of the factory is used to guess the class of the object by default, but it's possible to explicitly specify it:

import factory
from models import User

# This will guess the User class
class UserFactory(factory.Factory):
    first_name = 'John'
    last_name = 'Doe'
    admin = False

# This will use the User class (Admin would have been guessed)
class AdminFactory(factory.Factory):
    FACTORY_FOR = User

    first_name = 'Admin'
    last_name = 'User'
    admin = True

Using factories

factory_boy supports several different build strategies: build, create, attributes and stub:

# Returns a User instance that's not saved
user = UserFactory.build()

# Returns a saved User instance
user = UserFactory.create()

# Returns a dict of attributes that can be used to build a User instance
attributes = UserFactory.attributes()

# Returns an object with all defined attributes stubbed out:
stub = UserFactory.stub()

You can use the Factory class as a shortcut for the default build strategy:

# Same as UserFactory.create()
user = UserFactory()

The default strategy can be overridden:

UserFactory.default_strategy = factory.BUILD_STRATEGY
user = UserFactory()

The default strategy can also be overridden for all factories:

# This will set the default strategy for all factories that don't define a default build strategy
factory.Factory.default_strategy = factory.BUILD_STRATEGY

No matter which strategy is used, it's possible to override the defined attributes by passing keyword arguments:

# Build a User instance and override first_name
user = UserFactory.build(first_name='Joe')
user.first_name
# => 'Joe'

Lazy Attributes

Most factory attributes can be added using static values that are evaluated when the factory is defined, but some attributes (such as associations and other attributes that must be dynamically generated) will need values assigned each time an instance is generated. These "lazy" attributes can be added as follows:

class UserFactory(factory.Factory):
    first_name = 'Joe'
    last_name = 'Blow'
    email = factory.LazyAttribute(lambda a: '{0}.{1}@example.com'.format(a.first_name, a.last_name).lower())

UserFactory().email
# => 'joe.blow@example.com'

The function passed to LazyAttribute is given the attributes defined for the factory up to the point of the LazyAttribute declaration. If a lambda won't cut it, the lazy_attribute decorator can be used to wrap a function:

# Stub factories don't have an associated class.
class SumFactory(factory.StubFactory):
    lhs = 1
    rhs = 1

    @lazy_attribute
    def sum(a):
        result = a.lhs + a.rhs  # Or some other fancy calculation
        return result

Associations

Associated instances can also be generated using LazyAttribute:

from models import Post

class PostFactory(factory.Factory):
    author = factory.LazyAttribute(lambda a: UserFactory())

The associated object's default strategy is always used:

# Builds and saves a User and a Post
post = PostFactory()
post.id == None           # => False
post.author.id == None    # => False

# Builds and saves a User, and then builds but does not save a Post
post = PostFactory.build()
post.id == None           # => True
post.author.id == None    # => False

Inheritance

You can easily create multiple factories for the same class without repeating common attributes by using inheritance:

class PostFactory(factory.Factory):
    title = 'A title'

class ApprovedPost(PostFactory):
    approved = True
    approver = factory.LazyAttribute(lambda a: UserFactory())

Sequences

Unique values in a specific format (for example, e-mail addresses) can be generated using sequences. Sequences are defined by using Sequence or the decorator sequence:

class UserFactory(factory.Factory):
    email = factory.Sequence(lambda n: 'person{0}@example.com'.format(n))

UserFactory().email  # => 'person0@example.com'
UserFactory().email  # => 'person1@example.com'

Sequences can be combined with lazy attributes:

class UserFactory(factory.Factory):
    name = 'Mark'
    email = factory.LazyAttributeSequence(lambda a, n: '{0}+{1}@example.com'.format(a.name, n).lower())

UserFactory().email  # => mark+0@example.com