I happened to notice that if you look at
https://coverage.postgresql.org/src/backend/optimizer/util/predtest.c.gcov.html
it claims that the two occurrences of
elog(ERROR, "predicate_classify returned a bogus value");
at lines 492 and 803 are reached.
This would be quite astonishing if true, but it isn't true, since
the regression tests aren't reporting any such failure.
Needless to say, this puts quite a damper on my faith in the coverage
reports. Maybe that machine needs a software update?
regards, tom lane