--- /dev/null
+# in case we're (erroneously) running in parallel, give second.do some
+# time to start but not finish.
+echo 'first sleep' >&2
+sleep 1
+
+# Because of --shuffle, we can't be sure if first or second ran first, but
+# because all.do uses -j1, we *should* expect that if second ran first, it
+# at least ran to completion before we ran at all.
+if [ -e second.start ]; then
+ echo 'first: second already started before we did...' >&2
+ [ -e second.end ] || exit 21
+ echo 'first: ...and it finished as it should.' >&2
+ # no sense continuing the test; can't test anything if second already
+ # ran.
+ exit 0
+fi
+echo 'first: second has not started yet, good.' >&2
+
+echo 'first spin' >&2
+redo 1.a.spin
+[ -e 1.a.spin ] || exit 11
+echo 'first spin complete' >&2
+
+! [ -e second.start ] || exit 22