-spec attach_event_handlers(DestinationPID, Events) -> reference()
                         when DestinationPID :: pid(), Events :: [telemetry:event_name(), ...].

Attaches a "message" handler to the given events.

The attached handler sends a message to destination_pid every time it handles one of the events in events. The function returns a reference that you can use to make sure that messages come from this handler. This reference is also used as the handler ID, so you can use it to detach the handler with telemetry:detach/1.

The shape of messages sent to destination_pid is:

  {Event, Ref, Measurements, Metadata}

For example, in Erlang a test could look like this:

  Ref = telemetry_test:attach_event_handlers(self(), [[some, event]]),
  function_that_emits_the_event(),
  receive
      {[some, event], Ref, #{measurement := _}, #{meta := _}} ->
          telemetry:detach(Ref)
  after 1000 ->
      ct:fail(timeout_receive_attach_event_handlers)
  end.

In Elixir, a similar test would look like this:

  ref = :telemetry_test.attach_event_handlers(self(), [[:some, :event]])
  function_that_emits_the_event()
  assert_received {[:some, :event], ^ref, %{measurement: _}, %{meta: _}}