Improve test coverage for LISTEN/NOTIFY.
Back-patch commit
b10f40bf0 into older branches. This adds reporting
of NOTIFY messages to isolationtester.c, and extends the async-notify
test to include direct tests of basic NOTIFY functionality.
This provides useful infrastructure for testing a bug fix I'm about
to back-patch, and there seems no good reason not to have better tests
of LISTEN/NOTIFY in the back branches. The commit's survived long
enough in HEAD to make it unlikely that it will cause problems.
Back-patch as far as 9.6. isolationtester.c changed too much in 9.6
to make it sane to try to fix older branches this way, and I don't
really want to back-patch those changes too.
Discussion: https://postgr.es/m/31304.
1564246011@sss.pgh.pa.us