tests: harden

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1459846 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-4867: Allow custom SorterTemplates to override merge.


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1459851 13f79535-47bb-0310-9956-ffa450edef68