a question about TestAccumulator#testAccumBasic

[Zhang, Liyun]

Hi all:
  I have a question about  TestAccumulator#testAccumBasic.
 The first pig script: (TestAccumulator line 151~154)
  A = load '" + INPUT_FILE1 + "' as (id:int, fruit);
  B = group A by id;
  C = foreach B generate group,  
org.apache.pig.test.utils.AccumulatorBagCount(A);

  It uses org.apache.pig.test.utils.AccumulatorBagCount, in 
org.apache.pig.test.utils.AccumulatorBagCount#exec
  org.apache.pig.test.utils.AccumulatorBagCount#exec
public Integer exec(Tuple tuple) throws IOException {
        throw new IOException("exec() should not be called.");
}
My question:It should throw exception when script is excuted but why not throw 
exception?

The second script: (TestAccumulator line 169~171)
  A = load '" + INPUT_FILE1 + "' as (id:int, fruit);
 B = group A by id;
  C = foreach B generate group, 
org.apache.pig.test.utils.AccumulatorBagCount(A), 
org.apache.pig.test.utils.BagCount(A);
 It uses , org.apache.pig.test.utils.AccumulatorBagCount and ), 
org.apache.pig.test.utils.BagCount.
  The code checks whether if it throws exception, if not throw exception, the 
unit test fails.


TestAccumulator#testAccumBasic
@Test
    public void testAccumBasic() throws IOException{
    151    // test group by
    152    pigServer.registerQuery("A = load '" + INPUT_FILE1 + "' as (id:int, 
fruit);");
   153     pigServer.registerQuery("B = group A by id;");
    154    pigServer.registerQuery("C = foreach B generate group,  
org.apache.pig.test.utils.AccumulatorBagCount(A);");

        HashMap<Integer, Integer> expected = new HashMap<Integer, Integer>();
        expected.put(100, 2);
        expected.put(200, 1);
        expected.put(300, 3);
        expected.put(400, 1);

        Iterator<Tuple> iter = pigServer.openIterator("C");

        while(iter.hasNext()) {
            Tuple t = iter.next();
            assertEquals(expected.get((Integer)t.get(0)), (Integer)t.get(1));
        }

    169    pigServer.registerQuery("B = group A by id;");
    170   pigServer.registerQuery("C = foreach B generate group,  " +
                "org.apache.pig.test.utils.AccumulatorBagCount(A), 
org.apache.pig.test.utils.BagCount(A);");

        try{
            iter = pigServer.openIterator("C");

            while(iter.hasNext()) {
                Tuple t = iter.next();
                assertEquals(expected.get((Integer)t.get(0)), 
(Integer)t.get(1));
            }
            fail("accumulator should not be called.");
        }catch(IOException e) {
            // should throw exception from AccumulatorBagCount.
        }

        // test cogroup
        pigServer.registerQuery("A = load '" + INPUT_FILE1 + "' as (id:int, 
fruit);");
        pigServer.registerQuery("B = load '" + INPUT_FILE1 + "' as (id:int, 
fruit);");
        pigServer.registerQuery("C = cogroup A by id, B by id;");
        pigServer.registerQuery("D = foreach C generate group,  " +
                "org.apache.pig.test.utils.AccumulatorBagCount(A), 
org.apache.pig.test.utils.AccumulatorBagCount(B);");

        HashMap<Integer, String> expected2 = new HashMap<Integer, String>();
        expected2.put(100, "2,2");
        expected2.put(200, "1,1");
        expected2.put(300, "3,3");
        expected2.put(400, "1,1");

        iter = pigServer.openIterator("D");

        while(iter.hasNext()) {
            Tuple t = iter.next();
            assertEquals(expected2.get((Integer)t.get(0)), 
t.get(1).toString()+","+t.get(2).toString());
        }
    }

   Can anyone help me solving my question?

Best regards
Zhang,Liyun