### Question:
SeRequestSet implements Serializable { @Override public String toString() { return sortedRequests.size() + " SeRequest(s)"; } SeRequestSet(Set<SeRequest> seRequests);  SeRequestSet(SeRequest seRequest); void add(SeRequest seRequest); Set<SeRequest> getRequests(); SeRequest getSingleRequest(); @Override String toString();  }### Answer:
@Test public void toStringNull() { seRequestSet = new SeRequestSet(new HashSet<SeRequest>()); assertNotNull(seRequestSet.toString()); }