ExampleTest.java

package com.tynt.xiang;

import static org.junit.Assert.assertEquals;
import org.apache.pig.data.Tuple;
import org.junit.Before;
import org.junit.Test;
import com.tynt.xiang.helper.Helper;
import com.tynt.xiang.helper.PigRunner;


public class ExampleTest {
    private static final String BASE_DIR = "../scripts/example/";
    private static final String SCRIPT_FILE = BASE_DIR + "example.pig";
    private static final String OUT_FILE = "./target/pig-output";
    private static final String IN_FILE = "./target/test-classes/example-input.log";
    private PigRunner runner;
    
    @Before
    public void setUp() throws Exception {
        Helper.delete(OUT_FILE);
        runner = new PigRunner();
    }

    @Test
    public void testRecordCount() throws Exception {
    	runner.execute(SCRIPT_FILE, "in_file="+IN_FILE,"out_file="+OUT_FILE);

    	List<Tuple> tuples = runner.getTuples("some_pig_alias");
    	assertEquals(41, tuples.size());
    }
}

PigRunner.java

package com.tynt.xiang.helper;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import java.util.Iterator;

import org.apache.pig.ExecType;
import org.apache.pig.PigServer;
import org.apache.pig.data.Tuple;
import org.apache.pig.tools.parameters.ParameterSubstitutionPreprocessor;
import org.apache.pig.tools.parameters.ParseException;

public class PigRunner {
	private PigServer pigServer;
	
	public PigServer getPigServer() {
		return pigServer;
	}
	
	public PigRunner() throws Exception {
		pigServer = new PigServer(ExecType.LOCAL);
	}
	
	public void execute(String scriptFile, String... params) throws Exception {
		String substFile = preprocess(scriptFile, params);
		pigServer.registerScript(substFile); 
	}
	
	public List<Tuple> getTuples(String aliasName) throws IOException {
		List<Tuple> list = new ArrayList<Tuple>();
		
		Iterator<Tuple> tuples = pigServer.openIterator(aliasName);
		while(tuples.hasNext()) {
			Tuple t = tuples.next();
			list.add(t);
		}
		
		return list;
	}
	
	private String preprocess(String scriptFile, String... params)
			throws IOException, ParseException {

		ParameterSubstitutionPreprocessor psp = new ParameterSubstitutionPreprocessor(
				50);
		String substFile = scriptFile + ".subst";
		BufferedWriter writer = new BufferedWriter(new FileWriter(substFile));

		try {
			// String content = FileUtils.readFileToString(new File(script));
			// System.out.println(content);
			psp.genSubstitutedFile(new BufferedReader(
					new FileReader(scriptFile)), writer, params, null);
		} catch (org.apache.pig.tools.parameters.ParseException pex) {
			throw new ParseException(pex.getMessage());
		}

		return substFile;
	}
}

Run entire pig scripts from your JUnit tests just like you'll run them from the cluster/cmd line.

There's three new API in trunk for pig script which has parameters
registerScript(String fileName, Map<String,String> params)
registerScript(String fileName, List paramsFiles)
registerScript(String fileName, Map<String,String> params,List paramsFiles)

You can use that to replace your preprocess when you upgrade your pig