* @see Collectors#toSet()
* @see Collections#unmodifiableSet(java.util.Set)
*/
@Test public void setOfVotersInDistrictInUnmodifiableSet() throws ClassNotFoundException {
List<RegisteredVoter> allVoters = new ArrayList<>(asList(
new RegisteredVoter("CR2345"),
new RegisteredVoter("HA7654"),
new RegisteredVoter("HA2213"),
new RegisteredVoter("BA9987"),
new RegisteredVoter("CR6203"),
new RegisteredVoter("ED9876")
// ... and many more
));
Set<RegisteredVoter> votersInHackney = ElectoralDistrict.votersIn(HACKNEY, allVoters);