Person person1 = new Person(29, "Mircea");
Person person2 = new Person(29, "Manik");
first.put("k", person1);
assert firstCs.containsKey("k");
assert !secondCs.containsKey("k");
assert first.get("k").equals(person1);
assert second.get("k") == null;
second.put("k2", person2);
assert second.get("k2").equals(person2);