protected void makeAssertions(ImmutableBytesWritable key,
      Iterable<ImmutableBytesWritable> values) {
      int count = 0;
      for (ImmutableBytesWritable value : values) {
        String val = Bytes.toStringBinary(value.get());
        LOG.debug(
          "reduce: key[" + count + "] -> " + Bytes.toStringBinary(key.get()) + ", value -> " + val);
        if (first == null) first = val;
        last = val;
        count++;
      }
      assertEquals(3, count);
    }
Checks the last and first keys seen against the scanner boundaries.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/MultiTableInputFormatTestBase.java