Using FactoryBot with a PORO

# app/models/arrow_down.rb
class ArrowDown
  # Build an arrow beginning at @from and ending at @to
  # from |-╮ |
  #      | |  |
  #   to |<╯ |

  attr_reader :from, :to

  def initialize :from, :to
    @from = from
    @to = to
  end

  ...
  # Really cool, well written, arrow methods
  ...
end

# spec/factories/arrow_down_factory.rb
FactoryBot.define do
  factory :arrow_down, class: ArrowDown do
    from  { 0 }
    to    { 2 }

    initialize_with { new( from: from, to: to ) }
  end
end

# spec/models/arrow_down_spec.rb
require "rails_helper"

RSpec.describe ArrowDown, type: :model do
  let(:arrow_down) { FactoryBot.build(:arrow_down) }

  it "should point down" do
    expect(arrow_down.direction).to eq(:down)
  end
  ...
  # Really cool, well written, tests
  ...
end