"Mismatch in value class"迁移到 MapReduce 2 后，我的 reducer 单元测试抛出异常：
Mismatch in value class: expected: class org.apache.hadoop.io.IntWritable actual: class com.company.MyWritable
错误消息本身对我来说很清楚，但我不明白为什么 MRUnit 获得临时可写类而不是 IntWritable。
减速器实现：
public static class TestCountReduce extends
Reducer<Text, MyWritable, Text, IntWritable> {
public void reduce(Text key, Iterator<MyWritable> values,
Context context) throws IOException, InterruptedException {
...
context.write(key, new IntWritable(s.size()));
}
}
测试设置：
public void setUp() throws IOException {
Mapper<Object, Text, Text, MyWritable> mapper = new MyMapper();
Reducer<Text, MyWritable, Text, IntWritable> reducer = new MyReducer();
mapDriver = new MapDriver<Object, Text, Text, MyWritable>();
mapDriver.setMapper(mapper);
reduceDriver = new ReduceDriver<Text, MyWritable, Text, IntWritable>();
reduceDriver.setReducer(reducer);
}
最后是测试用例：
@Test
public void testReducer() throws IOException {
List<MyWritable> values = new ArrayList<MyWritable>();
values.add(new MyWritable("1"));
values.add(new MyWritable("1"));
reduceDriver.withInput(new Text("testkey"), values);
reduceDriver.withOutput(new Text("testkey"), new IntWritable(1));
reduceDriver.runTest();
}