bug.rb

 # frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails"#, github: "rails/rails", branch: "main"
end

require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = __dir__
  config.hosts << "example.org"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get "(/optional/:optional_id)/things" => "foo#foo", as: :things
  end
end

class TestController < ActionController::Base
  include Rails.application.routes.url_helpers

  def index
    render plain: "Home"
  end
end

require "minitest/autorun"
require "rack/test"

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_returns_success
    assert_equal "/things", app.routes.url_helpers.things_path(optional_id: false)
    assert_equal "/things", app.routes.url_helpers.things_path(false)
  end

  private
    def app
      Rails.application
    end
end