@SuppressWarnings("unchecked") // empty Object[] as E[]
  public static <E extends @Nullable Object> MinimalSet<E> of(E... contents) {
    return ofClassAndContents(Object.class, (E[]) new Object[0], Arrays.asList(contents));
  }

  @SuppressWarnings("unchecked") // empty Object[] as E[]
  public static <E extends @Nullable Object> MinimalSet<E> from(Collection<? extends E> contents) {

  /**
   * Creates a new, empty instance of the class under test.
   *
   * @return a new, empty map instance.
   * @throws UnsupportedOperationException if it's not possible to make an empty instance of the
   *     class under test.
   */
  protected abstract Map<K, V> makeEmptyMap() throws UnsupportedOperationException;

  /**
   * Creates a new, non-empty instance of the class under test.
   *

  }

  public static void assertEmpty(Iterable<?> iterable) {
    if (!isEmpty(iterable)) {
      fail("Not true that " + iterable + " is empty");
    }
  }

  public static void assertEmpty(Map<?, ?> map) {
    if (!map.isEmpty()) {
      fail("Not true that " + map + " is empty");
    }
  }

  public static void assertEqualInOrder(Iterable<?> expected, Iterable<?> actual) {

 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum CollectionSize implements Feature<Collection>, Comparable<CollectionSize> {
  /** Test an empty collection. */
  ZERO(0),
  /** Test a one-element collection. */
  ONE(1),
  /** Test a three-element collection. */
  SEVERAL(3),
  /*
   * TODO: add VERY_LARGE, noting that we currently assume that the fourth

    return populate(new HashMap<String, String>(), entries);
  }

  // TODO: call conversion constructors or factory methods instead of using
  // populate() on an empty map
  private static <T, M extends Map<T, String>> M populate(M map, Entry<T, String>[] entries) {
    for (Entry<T, String> entry : entries) {
      map.put(entry.getKey(), entry.getValue());
    }
    return map;