Hi Rudolf!

Oooh, I didn’t expect adding a handler within the test to end up that straightforward and clean! I’ve marked your answer as the solution because it does indeed solve the problem, thank you!

I’ve also extended your example helper slightly to improve the ergonomics, mainly so that it’s easy to get all the logged messages that match a given string, and to return a formatted version of the string (although I’m sure that there’s other cases that would be needed besides {:string, iolist} if this were to hit production:

defmodule LoggerTestHelper do
  def log(log_event, config) do
    message =
      case log_event.msg do
        {:string, iolist} -> to_string(iolist)
      end

    send(config.test_pid, {:logged_event, message, log_event})
  end

  def logs_containing_string(search_string) do
    {:messages, all_messages} = :erlang.process_info(self(), :messages)

    for {:logged_event, message, log_event} <- all_messages,
        String.contains?(message, search_string) do
      {message, log_event}
    end
  end
end

And here’s my example test:

test "logs with metadata", %{conn: conn} do
  {_result, _log} =
    ExUnit.CaptureLog.with_log(fn ->
      conn = get(conn, ~p"/posts")
      assert html_response(conn, 200) =~ "Listing Posts"
    end)

  assert [{message, log}] =
           LoggerTestHelper.logs_containing_string("Sent 200 for GET /posts")

  assert message =~ "2 queries executed in"
  assert message =~ "2 logs captured"

  assert log.meta.method == "GET"
  assert log.meta.request_path == "/posts"
  assert log.meta.duration
  assert log.meta.total_queries == 2

  for query <- log.meta.ecto_queries do
    assert query =~ "FROM \"posts\""
  end
end

If you’re curious about the content of the test I’ve been playing with the ideas of Wide Logs (or Canonical Logs) that are captured quite well in this Stripe blog post: