### Question:
PredicateCache { public String toString() { StringBuilder sb = new StringBuilder(); if (predicates != null) { sb.append(predicates.toString()); } if (containerProperties != null) { sb.append(containerProperties.toString()); } return sb.toString(); }  void add(STMT stmt); @SuppressWarnings("unchecked") Iterator<STMT> iterator(@Nullable UID predicate); boolean remove(STMT stmt); String toString();  }### Answer:
@Test public void ToString() { PredicateCache cache = new PredicateCache(); assertNotNull(cache.toString()); cache.add(new STMT(RDF.type, RDF.type, RDF.Property)); assertNotNull(cache.toString()); cache.add(new STMT(RDF.type, RDF.first, RDF.Property)); assertNotNull(cache.toString()); }