Using an anonymous subclass to test singleton objects in isolation

singleton_test_isolation.rb

class MySingletonClass
  include Singleton

  attr_reader :client

  def initialize
    @client = Service::We::Only::Ever::Need::One::Connection::To.new(SERVICE_URL)
  end
end

context MySingletonClass do
  setup do
    @singleton = Class.new(MySingletonClass)
  end

  # If we were to test the singleton object directly this test would fail if any other test previously initialized it
  test "creates a Service::We::Only::Ever::Need::One::Connection::To connection pointed at SERVICE_URL" do
    Service::We::Only::Ever::Need::One::Connection::To.expects(:new).with(SERVICE_URL)
    @singleton.instance
  end
end