You could try below by passing different log messages:

echo "2018-12-07  15:19:03" | logstash -e 'input { stdin {} } filter { date { match => [ "message", "yyyy-MM-dd  HH:mm:ss"] } }'

or you could make file with logs you would like to test.

cat file.log |  logstash -e 'input { stdin {} } filter { date { match => [ "message", "yyyy-MM-dd  HH:mm:ss"] } }'

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