MRUnit是对MapReduce程序进行单元测试的工具，可以对Mapper和Reducer程序分别进行测试。但是它没有集成在Hadoop安装环境中，如果想在开发MapReduce程序时使用这个工具，就需要自己安装。

MRUnit的安装

安装环境：

Eclipse版本为3.6.0

Hadoop版本为1.0.4

安装步骤：

（1）下载MRUnit，网址为http://mrunit.apache.org/，我下载的是 apache-mrunit-1.0.0-hadoop1-bin.tar.gz

（2）解压缩下载的文件，将lib目录下的hamcrest-core-1.1.jar，junit-4.10.jar，mockito-all-1.8.5.jar和mrunit-1.0.0-hadoop1.jar加入到Eclipse的项目中。

方法如下：选中待测试项目-->右键Buid Path-->Configure Buid Path-->点击Libraries-->点击Add External JARs  

MRUnit的使用

MaxTemperatureMapper.java，MaxTemperatureReducer.java，MaxTemperatureMapperTest.java，MaxTemperatureReducerTest.java

MaxTemperatureMapper.java

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class MaxTemperatureMapper 
	extends Mapper<LongWritable, Text, Text, IntWritable> {
	private static final int MISSING = 9999;
	
	public void map(LongWritable key, Text value, Context context)
		throws IOException, InterruptedException {
		String line = value.toString();
		String year = line.substring(15, 19);
		
		int airTemperature;
		if(line.charAt(87) == '+')
			airTemperature = Integer.parseInt(line.substring(88, 92));
		else
			airTemperature = Integer.parseInt(line.substring(87, 92));
		
		String quality = line.substring(92, 93);
		if(airTemperature != MISSING && quality.matches("[01459]"))
			context.write(new Text(year), new IntWritable(airTemperature));
	}
}

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class MaxTemperatureReducer
	extends Reducer<Text, IntWritable, Text, IntWritable> {
	
	public void reduce(Text key, Iterable<IntWritable> values, Context context) 
		throws IOException, InterruptedException {
		
		int maxValue = http://www.mamicode.com/Integer.MIN_VALUE;>
MaxTemperatureMapperTest.java
import java.io.IOException;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mrunit.mapreduce.MapDriver;
import org.junit.Test;

public class MaxTemperatureMapperTest {
	@Test
	public void processesValidRecord() throws IOException, InterruptedException {
		Text value = http://www.mamicode.com/new Text("0057332130999991950010103004+51317+028783FM-12+017199999V0203201N00721004501CN0100001N9-01281-01391102681");>
MaxTemperatureReducerTest.java
import java.io.IOException;
import java.util.Arrays;

import org.junit.Test;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mrunit.mapreduce.ReduceDriver;

public class MaxTemperatureReducerTest {
	@Test
	public void returnsMaximumIntegerInValues() throws IOException, InterruptedException {
		new ReduceDriver<Text, IntWritable, Text, IntWritable>()
			.withReducer(new MaxTemperatureReducer())
			.withInput(new Text("1950"), Arrays.asList(new IntWritable(10), new IntWritable(5)))
			.withOutput(new Text("1950"), new IntWritable(10))
			.runTest();
	}
}

需要注意程序中的@Test是不可或缺的

下面就可以运行测试程序了，如果要测试Mapper程序，那么就选中MaxTemperatureMapperTest.java，右键Run As-->JUnit Test，如果进度条为绿色，则表示测试正确，否则代表有错误。测试Reducer程序也是如此。
MRUnit的安装和使用