@cmaiacd Brazilian living in Berlin Bachelor of Computer Information System Coding since 2010 👵 Python 🐍 and Ruby 💎 Open Source and Community ❤ Conferences Backend Developer @ SoundCloud
@cmaiacd ● It is a fixtures replacement ● Based on factory_bot (Thoughtbot) ● First version: Django only ● Nowadays: framework-independent ● Unittest, Pytest...
@cmaiacd ❌ Fixtures: exhaustive test setup with every possible combination of corner cases ✅ Factories: objects customized for the current test, while only declaring the test-specific fields
@cmaiacd It offers many tools that help with the creation of the tests: ● Sequence ● Faker ● Fuzzy attributes ● LazyFunction ● LazyAttribute ● Inheritance ● Params ● Traits ● Strategies ● RelatedFactory/SubFactory
@cmaiacd Bad factories are like viruses ● Factories can get too tied ● Implicit errors might happen ● Factory usage involves a lot of copy/paste with small changes ● A poorly designed factory might affect many tests ● The tests are created in a way to fit the factory (factory-oriented testing) ● Developers bump into the same issue again and again ● The same hack has to be done several times
@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 ● 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 ● 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 ● Many tests depending on the same factory/fixture ● Tends to inflate the factory/fixture ● Hard to maintain ● Change a factory/fixture => tons of tests breaking ● Fixture/Factory-oriented testing
@cmaiacd 1. Factories should represent their models 2. Do not rely on defaults from factories 3. Factories should contain only the required data 4. Build over create 5. If FK is in the table: SubFactor If FK is in the other table: RelatedFactory + trait 6. Avoid sharing factories or fixtures among different files 7. Use fixtures to wrap factories to avoid duplication Review
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