This gem provides helper methods to FactoryBot to support memoization and reuse of factory created instances.

The goal is to clean up test code and speed up performance where your tests use models that have required associations but where those associations are not themselves referenced in the tests.

Example

For instance, suppose you have factories for a BlogPost model which has many Comments and each comment requires an associated User:

FactoryBot.define do
  factory :blog_post_ do
    title "Test Post"
    ...
  end
  
  factory :comment do
    body "Test comment"
    blog_post
    user
  end
  
  factory :user do
    name "Test User"
    ...
  end
end

Now if you need 30 comments for a blog post in your test:

  post = create(:blog_post)
  create_list(:comment, :blog_post => post)

However, this will create 30 unique User records which could be expensive if the User record has it's own required associations or performs several callbacks. A simple solution is to provide a single User record for all the Comments:

  post = create(:blog_post)
  user = create(:user)
  create_list(:comment, :blog_post => post, :user => user)

This gem provides an extension to the FactoryBot DSL so that you can accomplish the same thing at the factory level. This can help keep your test code clean since you don't have to declare additional variables that aren't relevant to the test.

  post = create(:blog_post)
  create_list(:comment, :blog_post => post, :user => any(:user))

The any method will return an object using the specified factory with default attributes. On the first invocation of any it will create the object; on subsequent calls it will return the same object.

You can also use the any method in your factory definitions so that the factory will re-use an associated record by default. This can make your tests much cleaner when the models get more complicated with layers of required associations. It can also help speed up a test suite that's already been written and gotten slower without having to rewrite every test case.

FactoryBot.define do
  factory :comment do
    body "Test comment"
    blog_post
    user { any(:user) }
  end
end

Note that you must include the any call inside a block in your factory so that it will only get evaluated at runtime. Be careful with this method, though, because it could slow down your test suite if you make use of the build method because the any defined objects will be inserted into the database.

Cleaning Up

You MUST cleanup the instantiated instances between tests or you will have random artifacts spanning them. Most test suites clear the database between runs so these artifacts will also be completely invalid. To do this you must call the clear_instances method. You can set up your test suite to do this before every test.

RSpec

Add this to your spec_helper.rb file:

RSpec.configure do |config|
  config.include FactoryBot::Syntax::Methods

  config.before do
    clear_instances
  end
end

Minitest::Spec

Add this to your test_helper.rb file:

class Minitest::Spec
  include FactoryBot::Syntax::Methods
  
  before do
    clear_instances
  end
end

ActiveSupport::TestCase

Add this to your test_helper.rb file:

class ActiveSupport::TestCase
  include FactoryBot::Syntax::Methods
  
  setup do
    clear_instances
  end
end

Minitest::Unit

Call FactoryBot.clear_instances in the setup method on all your test classes.

Helper Methods

All of these examples assume you've included FactoryBot::Syntax::Methods in your test helper. This gem adds the any and clear_instances methods to those helpers. If you don't include the helper methods, you must call FactoryBot.any and FactoryBot.clear_instances instead.

Parallelizing

This code is not compatible with multithreaded test runners. It will work fine with multi process test runners.