@SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "values is ImmutableSet")
  public Set<T> all() {
    return values;
  }
@Test
  public void shouldReturnAllValues() {
    // Given:
    CompatibleSet<CompatibleInteger> compatibleSet = new CompatibleSet<>(
        ImmutableSet.<CompatibleInteger>of(one, four));

    // When:
    Set<CompatibleInteger> all = compatibleSet.all();

    // Then:
    assertThat(all, containsInAnyOrder(one, four));
  }