sinatra_router.rb

class PathFinder
  attr_reader :paths

  def initialize(paths)
    @paths = paths
  end 

  def find(request_path)
    find_path(request_path) or fail ActiveRecord::RecordNotFound
  end 

  def find_path(request_path)
    paths.to_a.find do |path|
      request_path.match path_regex(path.name)
    end 
  end 

  def path_regex(path_name)
    Sinatra::Base.send(:compile, path_name).first
  end 

end

sinatra_router_spec.rb

require "rails_helper"
  
describe PathFinder do
  
  before do
    Fabricate(:path, name: "users")
    Fabricate(:path, name: "users/:user_id")
  end 
    
  let(:paths) { Path.all }
  subject { described_class.new(paths) }
  
  describe "#find" do
    it "finds the exact match" do
      expect(subject.find("users").name).to eq("users")
    end

    it "finds path with the colon(:) syntax" do
      expect(subject.find("users/6").name).to eq("users/:user_id")
    end

    it "fails when not found" do
      expect { subject.find("foo/bar") }.to raise_error ActiveRecord::RecordNotFound
    end
  end
end