Re: Testing LISTEN/NOTIFY more effectively

I wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
>> Perhaps we could just have isolationtester check to which
>> isolationtester session the backend pid belongs? And then print the
>> session name instead of the pid? That should be fairly easy, and would
>> probably give us all we need?

> Oh, that's a good idea -- it's already tracking all the backend PIDs,
> so probably not much extra work to do it like that.

I found out that to avoid confusion, one really wants the message to
identify both the sending and receiving sessions. Here's a patch
that does it that way and extends the async-notify.spec test to
perform basic end-to-end checks on LISTEN/NOTIFY.

I intentionally made the test show the lack of NOTIFY de-deduplication
that currently happens with subtransactions. If we change this as I
proposed in <17822(dot)1564186806(at)sss(dot)pgh(dot)pa(dot)us>, this test output will
change.

regards, tom lane