Create small test suite from master test suite in junit to use with pit (mutation)

I wanted to check the relationship between coverage and test suite effectiveness by creating a small test-suite out of master test suite by randomly picking the test-cases as described in this paper http://ift.tt/1YjpqFV and run the mutation test using pit for various sizes of test-suite. The SUT I am using is joda-time. I wrote the following program to create a small test-suite from master-suite

public class CustomTestAll extends TestCase {

public static Test suite() {
    List<Test> inter_list;
    List<Test> templist=new ArrayList<Test>();
    TestSuite j=null;
     Enumeration<Test> e;
    TestSuite suite = new TestSuite();
 ////   TestHours
     j= (TestSuite)TestHours.suite(); 
     e=j.tests();
     inter_list= Collections.list(e);


 ////TestDateTimeFieldType
     j= (TestSuite)TestDateTimeFieldType.suite(); 
     e=j.tests();
     templist = Collections.list(e);
     inter_list.addAll(templist);
     ////so on for all classes


     ///generating 10 unique random numbers between 0 and number of testcases
     List<Integer> list = new ArrayList<Integer>();
     for (int i=0; i<inter_list.size(); i++) {
         list.add(new Integer(i));
     }
     Collections.shuffle(list);

    for (int i = 0; i < 10;i++){
          suite.addTest(inter_list.get(list.get(i)));
    }
    Enumeration<Test> k=suite.tests();

    while(k.hasMoreElements()){System.out.println(k.nextElement());}

    return suite;

}}

This is running fine with junit and emma code coverage . However when I run mutation testing (pitest)using this test-suite, it is taking all the test-cases in a class instead of one selected. I am not able to figure what is wrong. I am a beginner in java and I am using eclipse.