@Test
  public void testMultiOutputFormatWithReduce() throws Throwable {
    Job job = new Job(mrConf, "MultiOutWithReduce");

    job.setMapperClass(WordCountMapper.class);
    job.setReducerClass(MultiOutWordCountReducer.class);
    job.setJarByClass(this.getClass());
    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputFormatClass(MultiOutputFormat.class);
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(IntWritable.class);

    JobConfigurer configurer = MultiOutputFormat.createConfigurer(job);

    configurer.addOutputFormat("out1", TextOutputFormat.class, IntWritable.class, Text.class);
    configurer.addOutputFormat("out2", SequenceFileOutputFormat.class, Text.class,
      IntWritable.class);
    configurer.addOutputFormat("out3", NullOutputFormat.class, Text.class,
      IntWritable.class);
    Path outDir = new Path(workDir.getPath(), job.getJobName());
    FileOutputFormat.setOutputPath(configurer.getJob("out1"), new Path(outDir, "out1"));
    FileOutputFormat.setOutputPath(configurer.getJob("out2"), new Path(outDir, "out2"));

    configurer.configure();

    String fileContent = "Hello World Hello World World";
    String inputFile = createInputFile(fileContent);
    FileInputFormat.setInputPaths(job, new Path(inputFile));

    Assert.assertTrue(job.waitForCompletion(true));

    Path textOutPath = new Path(outDir, "out1/part-r-00000");
    String[] textOutput = readFully(textOutPath).split("\n");
    Path seqOutPath = new Path(outDir, "out2/part-r-00000");
    SequenceFile.Reader reader = new SequenceFile.Reader(fs, seqOutPath, mrConf);
    Text key = new Text();
    IntWritable value = new IntWritable();
    String[] words = "Hello World".split(" ");
    Assert.assertEquals(words.length, textOutput.length);
    for (int i = 0; i < words.length; i++) {
      Assert.assertEquals((i + 2) + "\t" + words[i], textOutput[i]);
      reader.next(key, value);
      Assert.assertEquals(words[i], key.toString());
      Assert.assertEquals((i + 2), value.get());
    }
    Assert.assertFalse(reader.next(key, value));

  }
A word count test job that reads a input file and outputs the count of
words to a text file and sequence file with different key values.
hcatalog/core/src/test/java/org/apache/hive/hcatalog/mapreduce/TestMultiOutputFormat.java