private List<ShowLocksResponseElement> getLocks() throws Exception {
    return getLocks(txnMgr);
  }
SessionState is stored in ThreadLoacal; UnitTest runs in a single thread (otherwise Derby wedges)
{@link HiveTxnManager} instances are per SessionState.
So to be able to simulate concurrent locks/transactions s/o forking threads we just swap
the TxnManager instance in the session (hacky but nothing is actually threading so it allows us
to write good tests)
ql/src/test/org/apache/hadoop/hive/ql/lockmgr/TestDbTxnManager2.java