map = MutableClassToInstanceMap.create();
  }

  public void testConstraint() {
    /*
     * We'll give ourselves a pass on testing all the possible ways of breaking the constraint,
     * because we know that newClassMap() is implemented using ConstrainedMap which is itself
     * well-tested. A purist would object to this, but what can I say, we're dirty cheaters.
     */
    map.put(Integer.class, new Integer(5));