This is a followup to 037f9e07cd.
Reported by Mark H Weaver.
* gnu/tests/install.scm (%minimal-os): Pass a <marionette-configuration>
object as the value for the MARIONETTE-SERVICE-TYPE.
* gnu/services/mcron.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* gnu/tests/base.scm (%mcron-os, %test-mcron): New variables.
(run-mcron-test): New procedure.
* doc/guix.texi (Scheduled Job Execution): New node.
* gnu/tests.scm (<system-test>): New record type.
(write-system-test, test-modules, fold-system-tests)
(all-system-tests): New procedures.
* gnu/tests/base.scm (%test-basic-os): Turn into a <system-test>.
* gnu/tests/install.scm (%test-installed-os): Likewise.
* build-aux/run-system-tests.scm (%system-tests): Remove.
(run-system-tests): Use 'all-system-tests'.
* gnu/tests/base.scm (run-basic-test)["uname"]: Use the host name of OS.
["shepherd services"]: Use service names from OS.
(%test-basic-os): Add call to 'virtualized-operating-system'.