Set<Set<Integer>> powerSet = powerSet(elements);
    assertEquals(1, powerSet.size());
    assertEquals(ImmutableSet.of(ImmutableSet.of()), powerSet);
    assertEquals(0, powerSet.hashCode());
  }

  public void testPowerSetContents() {
    ImmutableSet<Integer> elements = ImmutableSet.of(1, 2, 3);
    Set<Set<Integer>> powerSet = powerSet(elements);
    assertEquals(8, powerSet.size());

border-bottom-radius(0);\n  }\n\n  > .btn:not(:first-child),\n  > .btn-group:not(:first-child) > .btn {\n    @include border-top-radius(0);\n  }\n}\n\n\n// Checkbox and radio options\n//\n// In order to support the browser's form validation feedback, powered by the\n// `required` attribute, we have to \"hide\" the inputs via `clip`. We cannot use\n// `display: none;` or `visibility: hidden;` as that also hides the popover.\n// Simply visually hiding the inputs via `opacity` would leave them clickable...

border-bottom-radius(0);\n  }\n\n  > .btn:not(:first-child),\n  > .btn-group:not(:first-child) > .btn {\n    @include border-top-radius(0);\n  }\n}\n\n\n// Checkbox and radio options\n//\n// In order to support the browser's form validation feedback, powered by the\n// `required` attribute, we have to \"hide\" the inputs via `clip`. We cannot use\n// `display: none;` or `visibility: hidden;` as that also hides the popover.\n// Simply visually hiding the inputs via `opacity` would leave them clickable...