factory_boy: testing like a pro. DjangoCon EU 2022

https://pretalx.evolutio.pt/djangocon-europe-2022/talk/XWUYA8/

Transcript

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

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

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3. @cmaiacd
   Who am I?
   

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4. @cmaiacd
   Backend Developer @
   

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5. @cmaiacd
   Brazilian 󰎙
   

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6. @cmaiacd
   Living in Berlin 󰎲
   

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7. @cmaiacd
   Queer 󰝲
   

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8. @cmaiacd
   󰘊 󰘋 🐶
   

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9. @cmaiacd
   Coding since 2010
   👵
   

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10. @cmaiacd
    Python 🐍 and Ruby
    💎
    

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11. @cmaiacd
    Community ❤
    

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12. @cmaiacd
    Conferences
    

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13. @cmaiacd
    Open Source ❤
    

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14. @cmaiacd
    Creator of ScanAPI
    

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15. @cmaiacd
    +1.5k
    + 1.2k ⭐
    

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16. @cmaiacd
    Workshop
    Tomorrow 4:55 PM
    󰠁󰳕
    

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17. @cmaiacd
    

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18. @cmaiacd
    factory_boy: what is it?
    

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19. @cmaiacd
    It is a fixtures replacement
    

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20. @cmaiacd
    Based on factory_bot (Thoughtbot)
    

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

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

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23. @cmaiacd
    

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

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25. @cmaiacd
    My Experience
    

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26. @cmaiacd
    +3 years
    Django Monolith
    🐘
    

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

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28. @cmaiacd
    

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29. @cmaiacd
    A poorly designed
    factory might affect
    many tests
    

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30. @cmaiacd
    Implicit errors
    

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

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32. @cmaiacd
    Factories can get too
    tied
    

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33. @cmaiacd
    Developers bump into
    the same issue again
    and again
    

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34. @cmaiacd
    Patterns 👀
    Best practices? 🤔
    

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35. @cmaiacd
    Demo App
    

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36. @cmaiacd
    Polls
    

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37. @cmaiacd
    Poll
    

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38. @cmaiacd
    Results
    

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39. @cmaiacd
    s
    

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40. @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
    

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41. @cmaiacd
    Model - Poll
    

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42. @cmaiacd
    Model - Poll
    

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43. @cmaiacd
    Model - Question
    

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44. @cmaiacd
    Model - Choice
    

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45. @cmaiacd
    Best Practices
    

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46. @cmaiacd
    1. FACTORIES SHOULD
    REPRESENT THEIR MODELS
    

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47. @cmaiacd
    Avoid implicit errors
    

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48. @cmaiacd
    BAD ❌
    

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49. @cmaiacd
    GOOD ✅
    

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50. @cmaiacd
    2. DO NOT RELY ON DEFAULTS
    FROM FACTORIES
    

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51. @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
    

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52. @cmaiacd
    BAD ❌
    

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53. @cmaiacd
    GOOD ✅
    

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54. @cmaiacd
    3. FACTORIES SHOULD
    CONTAIN ONLY THE REQUIRED
    DATA
    

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

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56. @cmaiacd
    BAD ❌
    

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57. @cmaiacd
    GOOD ✅
    

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58. @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.
    

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59. @cmaiacd
    4. BUILD OVER CREATE
    

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

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61. @cmaiacd
    BAD ❌
    

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62. @cmaiacd
    GOOD ✅
    

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

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

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65. @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
    

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66. @cmaiacd
    Good ✅
    

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

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68. @cmaiacd
    BAD ❌
    

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69. @cmaiacd
    GOOD ✅
    

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

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71. @cmaiacd
    Many tests depending
    on the same
    factory/fixture
    

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72. @cmaiacd
    Tends to inflate the
    factory/fixture
    

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73. @cmaiacd
    Hard to maintain
    

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

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75. @cmaiacd
    Fixture / Factory
    oriented testing
    

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

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

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78. @cmaiacd
    

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79. @cmaiacd
    Baby steps 🐣
    

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80. @cmaiacd
    Código
    

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81. @cmaiacd
    Official doc 📄
    factoryboy.readthedocs.io
    

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

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83. @cmaiacd
    Code
    github.com/FactoryBoy/
    factory_boy
    

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

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