hadoop版本：

$ hadoop versionHadoop 0.20.2-cdh3u4Subversion git://ubuntu-slave01/var/lib/jenkins/workspace/CDH3u4-Full-RC/build/cdh3/hadoop20/0.20.2-cdh3u4/source -r 214dd731e3bdb687cb55988d3f47dd9e248c5690Compiled by jenkins on Mon May  7 13:01:39 PDT 2012From source with checksum a60c9795e41a3248b212344fb131c12c

根据版本的不同采用的实现写法略有不同，此处采用的版本详情如下：

    	
     
      org.apache.mrunit
     	
     
      mrunit
     	
     
      1.0.0
     	
     
      hadoop1
     
    

其中常用的类如下：

org.apache.hadoop.mrunit.mapreduce.MapDriver;org.apache.hadoop.mrunit.mapreduce.MapReduceDriver;org.apache.hadoop.mrunit.mapreduce.ReduceDriver;

 mapper，combiner和reducer实现的含义描述如下：

CompMapper：把222-333##id1##id2 处理成key为id1##id2，value为1L(出现一次)CompCombiner：对相同的key进行累加CompReducer：吧key为id1##id2，value为long类型的数据进行累加然后除以某一个定值，以double的形式输出

 测试mapper，combiner和reducer的代码如下

private MapDriver
    
      mapDriver;private ReduceDriver
     
       reduceDriver;private ReduceDriver
      
        combinerDriver;private MapReduceDriver
       
         mapCombinerDriver;private MapReduceDriver
        
          mapReducerDriver;@Beforepublic void setUp() {	CompMapper mapper = new CompMapper();	CompCombiner combiner = new CompCombiner();	CompReducer reducer = new CompReducer();	mapDriver = new MapDriver
         
          (mapper); reduceDriver = new ReduceDriver
          
           (reducer); combinerDriver = new ReduceDriver
           
            (combiner); mapCombinerDriver = new MapReduceDriver
            
             ( mapper, combiner); mapReducerDriver = new MapReduceDriver
             
              ( mapper, reducer);}@Testpublic void testMapper() throws IOException { mapDriver.setInput(new Text("222-333##id1##id2"), new LongWritable(1L)); mapDriver.withOutput(new Text("id1##id2"), new LongWritable(1L)); mapDriver.runTest();}@Testpublic void testCombiner() throws IOException { List
              
                values = new ArrayList
               
                (); for (int i = 0; i < 5; i++) { values.add(new LongWritable(NumberUtils.toLong(i + ""))); } combinerDriver.addInput(new Text("id1##id2"), values); combinerDriver.withOutput(new Text("id1##id2"), new LongWritable(10L)); combinerDriver.runTest();}@Testpublic void testReducer() throws IOException { List
                
                  values = new ArrayList
                 
                  (); long count = 0; for (int i = 0; i < 5; i++) { count = count + (long) i; values.add(new LongWritable(NumberUtils.toLong(i + ""))); } reduceDriver.addInput(new Text("id1##id2"), values); int numHash = reduceDriver.getConfiguration().getInt( MinhashOptionCreator.NUM_HASH_FUNCTIONS, 10); DoubleWritable dw = new DoubleWritable(); BigDecimal b1 = new BigDecimal(count); BigDecimal b2 = new BigDecimal(numHash); dw.set(b1.divide(b2).doubleValue()); reduceDriver.withOutput(new Text("id1##id2"), dw); reduceDriver.runTest();}@Testpublic void tetMapCombiner() throws IOException { mapCombinerDriver.addInput(new Text("222-333##id1##id2"), new LongWritable(1L)); mapCombinerDriver.addInput(new Text("111-333##id1##id2"), new LongWritable(1L)); mapCombinerDriver.withOutput(new Text("id1##id2"), new LongWritable(2L)); mapCombinerDriver.runTest();}@Testpublic void tetMapReducer() throws IOException { mapReducerDriver.addInput(new Text("222-333##id1##id2"), new LongWritable(1L)); mapReducerDriver.addInput(new Text("111-333##id1##id2"), new LongWritable(1L)); int numHash = reduceDriver.getConfiguration().getInt( "NUM", 10); DoubleWritable dw = new DoubleWritable(); BigDecimal b1 = new BigDecimal(2L); BigDecimal b2 = new BigDecimal(numHash); dw.set(b1.divide(b2).doubleValue()); mapReducerDriver.withOutput(new Text("id1##id2"), dw); mapReducerDriver.runTest();}
                 
                
               
              
             
            
           
          
         
        
       
      
     
    

 注意事宜：

1.MRUnit与Hadoop的版本对应关系2.如果报java.lang.IncompatibleClassChangeError错那么就是版本的问题