(转)对mapreduce代码进行单元测试

（转）对mapreduce代码进行单元测试

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hadoop自带一个wordcount的示例代码，用于计算单词个数。我将其单独移出来，测试成功。源码如下：

package org.apache.hadoop.examples;
 
import java.io.IOException;
import java.util.StringTokenizer;
 
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;
 
public class WordCount {
 
  public static class TokenizerMapper 
       extends Mapper{
 
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
 
    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      StringTokenizer itr = new StringTokenizer(value.toString());
      while (itr.hasMoreTokens()) {
        word  = new Text(itr.nextToken()); //to unitest,should be new Text word.set(itr.nextToken())
        context.write(word, new IntWritable(1));
      }
    }
  }
 
  public static class IntSumReducer 
       extends Reducer {
    private IntWritable result = new IntWritable();
 
    public void reduce(Text key, Iterable values, 
                       Context context
                       ) throws IOException, InterruptedException {
      int sum = 0;
      for (IntWritable val : values) {
        sum += val.get();
      }
      result.set(sum);
      context.write(key, result);
    }
  }
 
  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err.println("Usage: wordcount  ");
      System.exit(2);
    }
    Job job = new Job(conf, "word count");
    job.setJarByClass(WordCount.class);
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

现在我想对其进行单元测试。一种方式，是job执行完了后，读取输出目录中的文件，确认计数是否正确。但这样的情况如果失败，也不知道是哪里失败。我们需要对map和reduce单独进行测试。
tomwhite的书《hadoop权威指南》有提到如何用Mockito进行单元测试，我们依照原书对温度的单元测试来对wordcount进行单元测试。(原书第二版的示例已经过时，可以参考英文版第三版或我的程序)。

package org.apache.hadoop.examples;
/* author zhouhh
 * date:2012.8.7
 */
import static org.mockito.Mockito.*;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
 
import org.apache.hadoop.io.*;
import org.junit.*;
 
public class WordCountTest {
 
	@Test
	public  void testWordCountMap() throws IOException, InterruptedException
	{
		WordCount w = new WordCount();
		WordCount.TokenizerMapper mapper = new WordCount.TokenizerMapper();
		Text value = new Text("a b c b a a");
		@SuppressWarnings("unchecked")
		WordCount.TokenizerMapper.Context context = mock(WordCount.TokenizerMapper.Context.class);
		mapper.map(null, value, context);
		verify(context,times(3)).write(new Text("a"), new IntWritable(1));
		verify(context).write(new Text("c"), new IntWritable(1));
		//verify(context).write(new Text("cc"), new IntWritable(1));
 
	}
 
	@Test
	public void testWordCountReduce() throws IOException, InterruptedException
	{
		WordCount.IntSumReducer reducer = new WordCount.IntSumReducer();
		WordCount.IntSumReducer.Context context = mock(WordCount.IntSumReducer.Context.class);
		Text key = new Text("a");
		List values = new ArrayList();
		values.add(new IntWritable(1));
		values.add(new IntWritable(1));
		reducer.reduce(key, values, context);
 
		verify(context).write(new Text("a"), new IntWritable(2));
 
	}
 
	public static void main(String[] args) {
//		try {
//			WordCountTest t = new WordCountTest();
//			
//			//t.testWordCountMap();
//			t.testWordCountReduce();
//		} catch (IOException e) {
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		} catch (InterruptedException e) {
//			// TODO Auto-generated catch block
//			e.printStackTrace();
//		}
 
	}
 
}

verify(context)只检查一次的写，如果多次写，需用verify(contex,times(n))检查,否则会失败。

执行时在测试文件上点run as JUnit Test，会得到测试结果是否通过。
本示例程序在hadoop1.0.3环境中测试通过。Mockito也在hadoop的lib中自带，打包在mockito-all-1.8.5.jar

参考：

http://bobflagg.com/blog/unit-testing-wordcount-mapreduce-example/

http://blog.pfa-labs.com/2010/01/unit-testing-hadoop-wordcount-example.html

 

注意：verify(context).SomeMethod(Arg1,Arg2...)中Arg如果是自定义类型务必实现equals方法，否则一直参数不匹配。