AbstractSymbol not hashable properly

AbstractSymbolTest.java

import static org.junit.Assert.*;

import java.util.Set;

import org.junit.Test;

import com.google.common.collect.Sets;


public class AbstractSymbolTest {

  @Test
  public void testHashSet() {
    Set<AbstractSymbol> set = Sets.newHashSet();
    AbstractSymbol symbol = new IdSymbol("test1", 5, 0);
    assertTrue(set.add(symbol));
    assertTrue(set.contains(symbol));
    assertFalse(set.add(symbol));
    AbstractSymbol symbol2 = (AbstractSymbol)symbol.clone();
    assertTrue(symbol.equals(symbol2));
    assertFalse(set.add(symbol2));
  }

}