@Test
  public void testHashTable() throws Exception {
    final TableName tableName = TableName.valueOf(name.getMethodName());
    final byte[] family = Bytes.toBytes("family");
    final byte[] column1 = Bytes.toBytes("c1");
    final byte[] column2 = Bytes.toBytes("c2");
    final byte[] column3 = Bytes.toBytes("c3");

    int numRows = 100;
    int numRegions = 10;
    int numHashFiles = 3;

    byte[][] splitRows = new byte[numRegions - 1][];
    for (int i = 1; i < numRegions; i++) {
      splitRows[i - 1] = Bytes.toBytes(numRows * i / numRegions);
    }

    long timestamp = 1430764183454L;
    // put rows into the first table
    Table t1 = TEST_UTIL.createTable(tableName, family, splitRows);
    for (int i = 0; i < numRows; i++) {
      Put p = new Put(Bytes.toBytes(i), timestamp);
      p.addColumn(family, column1, column1);
      p.addColumn(family, column2, column2);
      p.addColumn(family, column3, column3);
      t1.put(p);
    }
    t1.close();

    HashTable hashTable = new HashTable(TEST_UTIL.getConfiguration());

    Path testDir = TEST_UTIL.getDataTestDirOnTestFS(tableName.getNameAsString());

    long batchSize = 300;
    int code =
      hashTable.run(new String[] { "--batchsize=" + batchSize, "--numhashfiles=" + numHashFiles,
        "--scanbatch=2", tableName.getNameAsString(), testDir.toString() });
    assertEquals("test job failed", 0, code);

    FileSystem fs = TEST_UTIL.getTestFileSystem();

    HashTable.TableHash tableHash = HashTable.TableHash.read(fs.getConf(), testDir);
    assertEquals(tableName.getNameAsString(), tableHash.tableName);
    assertEquals(batchSize, tableHash.batchSize);
    assertEquals(numHashFiles, tableHash.numHashFiles);
    assertEquals(numHashFiles - 1, tableHash.partitions.size());
    for (ImmutableBytesWritable bytes : tableHash.partitions) {
      LOG.debug("partition: " + Bytes.toInt(bytes.get()));
    }

    ImmutableMap<Integer, ImmutableBytesWritable> expectedHashes =
      ImmutableMap.<Integer, ImmutableBytesWritable> builder()
        .put(-1, new ImmutableBytesWritable(Bytes.fromHex("714cb10a9e3b5569852980edd8c6ca2f")))
        .put(5, new ImmutableBytesWritable(Bytes.fromHex("28d961d9252ce8f8d44a07b38d3e1d96")))
        .put(10, new ImmutableBytesWritable(Bytes.fromHex("f6bbc4a224d8fd929b783a92599eaffa")))
        .put(15, new ImmutableBytesWritable(Bytes.fromHex("522deb5d97f73a414ecc11457be46881")))
        .put(20, new ImmutableBytesWritable(Bytes.fromHex("b026f2611aaa46f7110116d807545352")))
        .put(25, new ImmutableBytesWritable(Bytes.fromHex("39ffc1a3094aa12a2e90ffd9cef2ce93")))
        .put(30, new ImmutableBytesWritable(Bytes.fromHex("f6b4d75727ce9a30ac29e4f08f601666")))
        .put(35, new ImmutableBytesWritable(Bytes.fromHex("422e2d2f1eb79a8f02171a705a42c090")))
        .put(40, new ImmutableBytesWritable(Bytes.fromHex("559ad61c900fffefea0a15abf8a97bc3")))
        .put(45, new ImmutableBytesWritable(Bytes.fromHex("23019084513eca41cee436b2a29611cb")))
        .put(50, new ImmutableBytesWritable(Bytes.fromHex("b40467d222ddb4949b142fe145ee9edc")))
        .put(55, new ImmutableBytesWritable(Bytes.fromHex("372bf89fcd8ca4b7ab3c1add9d07f7e4")))
        .put(60, new ImmutableBytesWritable(Bytes.fromHex("69ae0585e6255de27dce974e332b8f8b")))
        .put(65, new ImmutableBytesWritable(Bytes.fromHex("8029610044297aad0abdbecd485d8e59")))
        .put(70, new ImmutableBytesWritable(Bytes.fromHex("de5f784f7f78987b6e57ecfd81c8646f")))
        .put(75, new ImmutableBytesWritable(Bytes.fromHex("1cd757cc4e1715c8c3b1c24447a1ec56")))
        .put(80, new ImmutableBytesWritable(Bytes.fromHex("f9a53aacfeb6142b08066615e7038095")))
        .put(85, new ImmutableBytesWritable(Bytes.fromHex("89b872b7e639df32d3276b33928c0c91")))
        .put(90, new ImmutableBytesWritable(Bytes.fromHex("45eeac0646d46a474ea0484175faed38")))
        .put(95, new ImmutableBytesWritable(Bytes.fromHex("f57c447e32a08f4bf1abb2892839ac56")))
        .build();

    Map<Integer, ImmutableBytesWritable> actualHashes = new HashMap<>();
    Path dataDir = new Path(testDir, HashTable.HASH_DATA_DIR);
    for (int i = 0; i < numHashFiles; i++) {
      Path hashPath = new Path(dataDir, HashTable.TableHash.getDataFileName(i));

      MapFile.Reader reader = new MapFile.Reader(hashPath, fs.getConf());
      ImmutableBytesWritable key = new ImmutableBytesWritable();
      ImmutableBytesWritable hash = new ImmutableBytesWritable();
      while (reader.next(key, hash)) {
        String keyString = Bytes.toHex(key.get(), key.getOffset(), key.getLength());
        LOG.debug("Key: " + (keyString.isEmpty() ? "-1" : Integer.parseInt(keyString, 16))
          + " Hash: " + Bytes.toHex(hash.get(), hash.getOffset(), hash.getLength()));

        int intKey = -1;
        if (key.getLength() > 0) {
          intKey = Bytes.toInt(key.get(), key.getOffset(), key.getLength());
        }
        if (actualHashes.containsKey(intKey)) {
          Assert.fail("duplicate key in data files: " + intKey);
        }
        actualHashes.put(intKey, new ImmutableBytesWritable(hash.copyBytes()));
      }
      reader.close();
    }

    FileStatus[] files = fs.listStatus(testDir);
    for (FileStatus file : files) {
      LOG.debug("Output file: " + file.getPath());
    }

    files = fs.listStatus(dataDir);
    for (FileStatus file : files) {
      LOG.debug("Data file: " + file.getPath());
    }

    if (!expectedHashes.equals(actualHashes)) {
      LOG.error("Diff: " + Maps.difference(expectedHashes, actualHashes));
    }
    Assert.assertEquals(expectedHashes, actualHashes);

    TEST_UTIL.deleteTable(tableName);
    TEST_UTIL.cleanupDataTestDirOnTestFS();
  }
Basic test for the HashTable M/R tool
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/TestHashTable.java