tests: improve test

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1545011 13f79535-47bb-0310-9956-ffa450edef68
tests: harden test

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1545014 13f79535-47bb-0310-9956-ffa450edef68