The reason for the xcheck (xtests) distinction is that these are tests that
cannot always be run, especially in build systems and the like.
Some require network connectivity. Others might require some special setup
on the local system or some privilege or something like that. There are
only a handful of them. I haven't seen any with clear comments explaining
what their requirements are. Someone should go through and figure out each
case and document its details. It may be appropriate for developers to run
xcheck as well as check, but we need to get clear on the individual tests'
requirements before we can be sure.
It would be wrong to have 'make check' run these tests. If a test can be
run safely in all circumstances, it belongs in tests rather than xtests.