Three ways to do STI factories

one.rb

# assets.rb
FactoryBot.define do
  factory(:asset) do
    # definition
  end
end

# audio_assets.rb
FactoryBot.define do
  factory(:audio_asset, parent: :asset, class: AudioAsset) do
    # definition
  end
end

three.rb

# assets.rb
FactoryBot.define do
  trait(:asset) do
    # definition
  end
  
  factory(:audio_asset, traits: %i[asset]) do
    # definition
  end
  
  # other subclasses, like video_asset, defined here too
end

two.rb

# shared_traits.rb
FactoryBot.define do
  trait(:asset) do
    # definition
  end
end

# audio_assets.rb
FactoryBot.define do
  factory(:audio_asset) do
    asset # Ambiguous: you have to know this is a trait, not an association
  end
end