tests: harden

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1459848 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-4867: Allow custom SorterTemplates to override merge (merged from r1459851).


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1459853 13f79535-47bb-0310-9956-ffa450edef68