Add a test case for
a316a3bc
a316a3bc fixed the code in build_simpl_rel() that propagates
RelOptInfo.userid from parent to child rels so that it works
correctly for the child rels of a UNION ALL subquery rel, though
no tests were added in that commit. So do so here.
As noted in the discussion, coming up with a test case in the core
regression suite for this fix has turned out to be tricky, so the
test case is added to the postgres_fdw's suite instead.
postgresGetForeignRelSize()'s use of user mapping for the user
specified in RelOptInfo.userid makes it relatively easier to craft
a test case around.
Discussion: https://postgr.es/m/CA%2BHiwqH91GaFNXcXbLAM9L%3DzBwUmSyv699Mtv3i1_xtk9Xec_A%40mail.gmail.com
Backpatch-through: 16