這個功能好像是CDH那邊開發的。。。

1.  首先下載jar包：hadoop-0.21.0-mrunit.jar。（經測試，這個jar包是關聯舊API的。請自己根據情況決定）

2.  在eclipse的build path中加入此jar包。

3.  編寫測試程式：

package unittest;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mrunit.ReduceDriver;
import org.junit.Before;
import org.junit.Test;


@SuppressWarnings("all")
public class ReducerTest {
	
	public static class ReducerClass implements Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable intvalue = new IntWritable(0);
		@Override
		public void configure(JobConf job) {
			job.setJobName("test");
			System.err.println("in configure method");
			System.out.println("job name is set to: ---------preset--------" +
					"------------------------" + job.getJobName());
//			System.out.println("job.getJobEndNotificationURI() -----" +
//					"-----preset------------" + job.getJobEndNotificationURI());
//			System.out.println("job.getJobLocalDir() -----" +
//					"------preset-----------" + job.getJobLocalDir());
//			System.out.println("job.getJobPriority() -----" +
//					"------preset-----------" + job.getJobPriority());
		}

		@Override
		public void close() throws IOException {
			System.err.println("in close method");
		}

		@Override
		public void reduce(Text key, Iterator<IntWritable> values,
				OutputCollector<Text, IntWritable> output, Reporter reporter)
				throws IOException {
			int sum = 0;
			while (values.hasNext()) {
				sum += values.next().get();
			}
			intvalue.set(sum);
			output.collect(key, intvalue);
		}

		
	}
	
	private Reducer reducer;
	private ReduceDriver reducerDriver;
	@Before
	public void init() {
		reducer = new ReducerClass();
		reducerDriver = new ReduceDriver(reducer);
	}
	
	@Test
	public void test() {
		String key = "key";
		List values = new ArrayList();
		values.add(new IntWritable(5));
		values.add(new IntWritable(3));
		
		reducerDriver.withInput(new Text(key), values)
					 .withOutput(new Text("key"), new IntWritable(8))
					 .runTest();
	}	
	
}