tests: improve test

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1545010 13f79535-47bb-0310-9956-ffa450edef68
tests: harden test

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1545013 13f79535-47bb-0310-9956-ffa450edef68