junit junit.framework.testsuite - runnable methods

i've finished section tests (in exam class). educational i've review conspicuous i should testsuite unittests.

odd i'm controlling section exam directly (selecting exam category - run junit test) all operative fine, altough i'm perplexing same thing exam unit there's always an exception: java.lang.exception: runnable methods.

here formula exam suite:

import junit.framework.test;
import junit.framework.testsuite;

public category alltests {

public stationary exam suite() {
    testsuite unit = new testsuite("test unit com.xxx.yyyy.test");
    //$junit-begin$
    suite.addtestsuite(testcase.class);
    //$junit-end$
    relapse suite;
    }

}

any ideas since isn't operative ?