defer_test.rb

  def test_defer_raise
    scheduler = RX::TestScheduler.new 

    invoked = 0
    err = 'foo'

    res = scheduler.configure do 
      RX::Observable.defer do
        invoked += 1
        raise err
      end
    end

    puts res.messages.to_s
    msgs = [on_error(200, err)]
    assert_messages msgs, res.messages    

    assert_equal 1, invoked     
  end

result.txt

[#<struct RX::Recorded time=200, value=on_error(private method `raise' called for Module:Class)>]