public void makeAssertions(ImmutableBytesWritable key, Result value) throws IOException {
      if (value.size() != 1) {
        throw new IOException("There should only be one input column");
      }
      Map<byte[], NavigableMap<byte[], NavigableMap<Long, byte[]>>> cf = value.getMap();
      if (!cf.containsKey(INPUT_FAMILY)) {
        throw new IOException(
          "Wrong input columns. Missing: '" + Bytes.toString(INPUT_FAMILY) + "'.");
      }
      String val = Bytes.toStringBinary(value.getValue(INPUT_FAMILY, null));
      LOG.debug("map: key -> " + Bytes.toStringBinary(key.get()) + ", value -> " + val);
    }
Pass the key and value to reduce.
@param key     The key, here "aaa", "aab" etc.
@param value   The value is the same as the key.
@param context The task context.
@throws IOException When reading the rows fails.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/MultiTableInputFormatTestBase.java