tests: add script output buffering race check

Regression check to a fix by Stanislav Brabec.

Reference: 0b285b84b2
CC: Stanislav Brabec <sbrabec@suse.cz>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

tests/expected/script/buffering-race

@@ -0,0 +1,3 @@
+Script started, file is /dev/null
+Hallo World
+Script done, file is /dev/null

tests/ts/script/buffering-race

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# This file is part of util-linux.
+#
+# This file is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This file is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+TS_TOPDIR="${0%/*}/../.."
+TS_DESC="buffering race"
+
+. $TS_TOPDIR/functions.sh
+ts_init "$*"
+
+ts_check_test_command "$TS_CMD_SCRIPT"
+
+$TS_CMD_SCRIPT -c "echo Hallo World" /dev/null </dev/null >$TS_OUTPUT
+
+ts_finalize
+