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testland/factory-bot-data

Authors Ruby FactoryBot factories with traits, associations, sequences, and the three build strategies (build / create / build_stubbed); integrates with RSpec / Minitest test suites; pairs with Faker for randomized field values. Use when the project is Ruby / Rails and needs structured fixture creation with referential integrity.

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strategies-and-anti-patterns.mdreferences/

FactoryBot build strategies and anti-patterns

Reference detail for factory-bot-data: the three build strategies and the factory anti-pattern catalog.

Build strategies

Per factory_bot-readme, FactoryBot supports three:

StrategyWhat it doesWhen to use
build(:x)Returns an unsaved ActiveRecord object.Pure-logic tests; no DB persistence needed.
create(:x)Saves the object (and any associations) to the database.Integration tests that exercise persistence.
build_stubbed(:x)Returns a stubbed object: appears persisted (new_record? returns false) but never hits the database.Speed up unit tests that don't actually need DB IO.

Speed hierarchy: build_stubbed >> build >> create. Use the weakest one that still tests what you need.

build(:user)          # Unsaved User instance
create(:user)         # Persisted User (and any associations)
build_stubbed(:user)  # Fake-persisted User; `id` is set, `new_record?` is false

Anti-patterns

Anti-patternWhy it failsFix
FactoryBot.create(:user) in every test, even for read-only assertionsDatabase overhead per test; suite slows linearly with test count.Use build_stubbed for unit tests that don't exercise persistence; reserve create for integration tests.
One mega-factory with 30 attributes in the baseEvery create(:user) writes 30 columns; tests that need 3 attributes pay the cost.Minimal base factory + traits for the rich variants.
Per-test-class factory definitionsTwo test files re-define :user differently; subtle bug.One factory per class, in spec/factories/ (auto-loaded by factory_bot_rails).
sequence for fields that should be random (e.g. names)Sequence values are predictable; tests pass on User 1 User 2 patterns that wouldn't pass on real names.Use Faker for value variety, sequence for uniqueness only.
create_list(:user, 100) per testDB write storm; even fast tests stall on bulk insert.Use build_stubbed_list if persistence isn't required; if it is, use raw SQL bulk insert.
Factory associations that always create the parentA test of Post creates a User; that creates 5 Permissions; etc. - explosion of objects.Pass an existing parent: create(:post, user: existing_user).

references

strategies-and-anti-patterns.md

SKILL.md

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