factory_boy: testing like a pro. DjangoCon EU 2022

@cmaiacd factory_boy DjangoCon EU 2022 - Porto 󰐨 Camila Maia
testing like a pro

@cmaiacd You can ﬁnd this presentation at: speakerdeck.com/cmaiacd

@cmaiacd Who am I?

@cmaiacd Backend Developer @

@cmaiacd Brazilian 󰎙

@cmaiacd Living in Berlin 󰎲

@cmaiacd Queer 󰝲

@cmaiacd 󰘊 󰘋 🐶

@cmaiacd Coding since 2010 👵

@cmaiacd Python 🐍 and Ruby 💎

@cmaiacd Community ❤

@cmaiacd Conferences

@cmaiacd Open Source ❤

@cmaiacd Creator of ScanAPI

@cmaiacd +1.5k + 1.2k ⭐

@cmaiacd Workshop Tomorrow 4:55 PM 󰠁󰳕

@cmaiacd

@cmaiacd factory_boy: what is it?

@cmaiacd It is a ﬁxtures replacement

@cmaiacd Based on factory_bot (Thoughtbot)

@cmaiacd First version: Django only Nowadays: framework-independent Unittest, Pytest...

@cmaiacd For complex objects: ❌ Fixtures: static, hard to maintain
✅ Factories: easy-to-use

@cmaiacd

@cmaiacd 🧰 🛠 🔧 ⚙ Sequence Faker Fuzzy attributes LazyFunction
LazyAttribute Inheritance Inheritance Params Traits Strategies RelatedFactory / SubFactory

@cmaiacd My Experience

@cmaiacd +3 years Django Monolith 🐘

@cmaiacd +230 tables +2200 relevant ﬁles +75k relevant lines

@cmaiacd

@cmaiacd A poorly designed factory might affect many tests

@cmaiacd Implicit errors

@cmaiacd The tests are created in a way to ﬁt
the factory factory-oriented testing

@cmaiacd Factories can get too tied

@cmaiacd Developers bump into the same issue again and again

@cmaiacd Patterns 👀 Best practices? 🤔

@cmaiacd Demo App

@cmaiacd Polls

@cmaiacd Poll

@cmaiacd Results

@cmaiacd s

@cmaiacd Model - Poll Poll Question Choice n:1 pub_date :
DateTimeField premium : BooleanField author : CharField question_text : CharField language : CharField choice_text : CharField votes : IntegerField 1:1

@cmaiacd Model - Poll

@cmaiacd Model - Question

@cmaiacd Model - Choice

@cmaiacd Best Practices

@cmaiacd 1. FACTORIES SHOULD REPRESENT THEIR MODELS

@cmaiacd Avoid implicit errors

@cmaiacd BAD ❌

@cmaiacd GOOD ✅

@cmaiacd 2. DO NOT RELY ON DEFAULTS FROM FACTORIES

@cmaiacd • If a default value is changed, all tests
that depend on it will break • The setup of a test should contain all the logic to ensure it will always pass • Explicit better than implicit

@cmaiacd BAD ❌

@cmaiacd GOOD ✅

@cmaiacd 3. FACTORIES SHOULD CONTAIN ONLY THE REQUIRED DATA

@cmaiacd If the ﬁeld is nullable (null=True) the attribute should
be under a trait and not as a default value

@cmaiacd BAD ❌

@cmaiacd GOOD ✅

@cmaiacd If we want to have an author, we can
use PollFactory(with_author=True) now When are we going to remember to test the case PollFactory(author=None)? We should not assume there is an author when DB actually allows to not have it.

@cmaiacd 4. BUILD OVER CREATE

@cmaiacd MyFactory.build() creates a local object (memory) MyFactory.create() creates a
local object + stores it in the DB

@cmaiacd BAD ❌

@cmaiacd GOOD ✅

@cmaiacd BUILD STRATEGY ========== 14 passed in 1.76 seconds ==========
CREATE STRATEGY ========== 14 passed in 3.26 seconds ==========

@cmaiacd 5. IF FK IS IN THE TABLE: SUBFACTOR IF
FK IS IN THE OTHER TABLE: RELATEDFACTORY + TRAIT

@cmaiacd SubFactory: builds/creates the SubFactory during the process of creation
of the main factory RelatedFactory: builds/creates the RelatedFactory after creating the main factory

@cmaiacd Good ✅

@cmaiacd 6. USE FIXTURES TO WRAP FACTORIES TO AVOID DUPLICATION

@cmaiacd BAD ❌

@cmaiacd GOOD ✅

@cmaiacd 7. AVOID SHARING FACTORIES OR FIXTURES AMONG DIFFERENT FILES

@cmaiacd Many tests depending on the same factory/ﬁxture

@cmaiacd Tends to inﬂate the factory/ﬁxture

@cmaiacd Hard to maintain

@cmaiacd Change a factory/ﬁxture… tons of tests breaking

@cmaiacd Fixture / Factory oriented testing

@cmaiacd Ok, ok, I got it! 😌 Now I know
the best practices 💪

@cmaiacd So let’s try to ﬁx one ﬁrst factory… 🤓

@cmaiacd

@cmaiacd Baby steps 🐣

@cmaiacd Código

@cmaiacd Oﬃcial doc 📄 factoryboy.readthedocs.io

@cmaiacd Common recipes 󰠉 factoryboy.readthedocs.io/ en/stable/recipes.html

@cmaiacd Code github.com/FactoryBoy/ factory_boy

@cmaiacd THANK YOU! MUITO OBRIGADA! @cmaiacd camilamaia 󰠁 cmaiacd.com

factory_boy: testing like a pro. DjangoCon EU 2022

factory_boy: testing like a pro. DjangoCon EU 2022

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