Previous testcase redirects echo-out into /dev/null
using "&>" as below

echo "trigger-command" >> trigger &> /dev/null

But this means redirecting both stdout and stderr into
/dev/null because it is same as below

echo "trigger-command" >> trigger > /dev/null 2>&1

So ">> trigger" redirects stdout to trigger file, but
next "> /dev/null" redirects stdout to /dev/null again
and the last "2>/&1" redirects stderr to stdout (/dev/null)

This fixes it by "2> /dev/null". And also, since it
must fail, add "!" to echo command.

Fixes: f06eec4d0f2c ("selftests: ftrace: Add inter-event hist triggers 
testcases")
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
 .../inter-event/trigger-extended-error-support.tc  |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git 
a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
 
b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
index 786dce7e48be..2aabab363cfb 100644
--- 
a/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
+++ 
b/tools/testing/selftests/ftrace/test.d/trigger/inter-event/trigger-extended-error-support.tc
@@ -29,7 +29,7 @@ do_reset
 
 echo "Test extended error support"
 echo 'hist:keys=pid:ts0=common_timestamp.usecs if comm=="ping"' > 
events/sched/sched_wakeup/trigger
-echo 'hist:keys=pid:ts0=common_timestamp.usecs if comm=="ping"' >> 
events/sched/sched_wakeup/trigger &>/dev/null
+! echo 'hist:keys=pid:ts0=common_timestamp.usecs if comm=="ping"' >> 
events/sched/sched_wakeup/trigger 2> /dev/null
 if ! grep -q "ERROR:" events/sched/sched_wakeup/hist; then
     fail "Failed to generate extended error in histogram"
 fi

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