public void delAtTimestamp(String qual, long ts) {
    del.addColumn(FAMILY_BYTES, Bytes.toBytes(qual), ts);
    logDelete(qual, ts, "at");
  }
Disable this when this test fails hopelessly and you need to debug a simpler case.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestSeekOptimizations.java