multi_factory

Define a single factory to generate the same data in multiple formats:

• Base (original data as defined on the factory)
• JSON (original data converted into a Python dict that is JSON serialisable)
• Domain (JSON data that is passed through a marshmallow schema that validates it and converts it into a domain object like a @dataclass)

Installation

multi_factory can be installed using pip (requires Python >=3.10):

pip install multi-factory

Quick start

Imagine you have the following code to represent a User in your application:

from typing import Any
from enum import Enum
from uuid import UUID
from datetime import datetime
from dataclasses import dataclass
from marshmallow import Schema, fields, post_load


class Gender(Enum):
    MALE = 1
    FEMALE = 2
    OTHER = 3


class UserSchema(Schema):
    id = fields.UUID()
    first_name = fields.String()
    last_name = fields.String()
    age = fields.Integer()
    birthday = fields.DateTime()
    gender = fields.Enum(Gender)

    @post_load
    def to_domain(self, incoming_data: dict[str, Any], **kwargs: Any) -> User:
        return User(**incoming_data)


@dataclass
class User:
    id: UUID
    first_name: str
    last_name: str
    age: int
    birthday: datetime
    gender: Gender

The above code will be used in a POST /users HTTP API endpoint, where the request body will contain a JSON representation of the User class that will need to be validated and de-serialized by the UserSchema class. The UserSchema class will also pass the validated data into the User class so it is easier to use and pass around your application.

To be able to test this POST /users endpoint, you will need to define factories to generate data for this User class in multiple formats for use in tests.

You write the following code to define multiple independent factories to achieve this:

import factory
from uuid import uuid4


class UserDictFactory(factory.Factory):
    class Meta:
        model = dict

    id = uuid4()
    first_name = "Bob"
    last_name = "Dylan"
    age = 21
    birthday = datetime(year=2000, month=1, day=1, hour=0)
    gender = Gender.MALE


class UserJSONFactory(factory.Factory):
    class Meta:
        model = dict

    id = str(uuid4())
    first_name = "Bob"
    last_name = "Dylan"
    age = 21
    birthday = datetime(year=2000, month=1, day=1, hour=0).isoformat()
    gender = Gender.MALE.name


class UserDomainFactory(factory.Factory):
    class Meta:
        model = User

    id = uuid4()
    first_name = "Bob"
    last_name = "Dylan"
    age = 21
    birthday = datetime(year=2000, month=1, day=1, hour=0)
    gender = Gender.MALE

Having to write 3 factories here adds more work that what should be necessary. It also increases the risk of these 3 factories getting out of sync if a change is made to one of them and not the other 2.

With multi-factory, we can do the following instead:

from multi_factory import JSONToDomainFactory


class UserFactory(JSONToDomainFactory[User, UserSchema]):
    id = uuid4()
    first_name = "Bob"
    last_name = "Dylan"
    age = 21
    birthday = datetime(year=2000, month=1, day=1, hour=0)
    gender = Gender.MALE

This UserFactory combines the 3 factories above into a single factory. This means you only need to define the test data once, which requires less maintenance that having the same data defined in multiple factories.

When you invoke this UserFactory you will have access to the 3 different formats for the same data:

>>> result = UserFactory()
>>> result
JSONToDomainFactoryResult(
    base={
        'id': UUID('96a43fc4-069a-4882-a388-24033299496f'), 
        'first_name': 'Bob', 
        'last_name': 'Dylan', 
        'age': 21, 
        'birthday': datetime.datetime(2000, 1, 1, 0, 0), 
        'gender': <Gender.MALE: 1>
    }, 
    json={
        'id': '96a43fc4-069a-4882-a388-24033299496f', 
        'first_name': 'Bob', 
        'last_name': 'Dylan', 
        'age': 21, 
        'birthday': '2000-01-01T00:00:00', 
        'gender': 'MALE'
    }, 
    domain=User(
        id=UUID('96a43fc4-069a-4882-a388-24033299496f'), 
        first_name='Bob', 
        last_name='Dylan', 
        age=21, 
        birthday=datetime.datetime(2000, 1, 1, 0, 0), 
        gender=<Gender.MALE: 1>
    )
)