How huge does mvtest_huge need to be?

Continuing to investigate possible speedups of the regression tests,
I noticed that some of the slower individual statements are those
dealing with mvtest_huge and mvtest_hugeview in matview.sql.
Cutting the size of mvtest_huge from 100K rows to 10K rows is enough
to halve the overall runtime of matview.sql, at least on the relatively
slow buildfarm animal I was checking this on.

I was going to propose doing that, but then looking at commit b69ec7cc9
which introduced these tables, I began to wonder why they're large at all.
Even a one-row matview would have been enough to test for the bug that
that commit fixed.

So ... is there a good reason to be using a large table here, and
if so what is it, and how big does the table really need to be
to provide useful test coverage?

regards, tom lane