Set<Set<Integer>> reverse = powerSet(ImmutableSet.copyOf(elements.asList().reverse()));
    new EqualsTester().addEqualityGroup(forward, reverse).testEquals();
  }

  /**
   * Test that a hash code miscomputed by "input.hashCode() * tooFarValue / 2" is correct under our
   * {@code hashCode} implementation.
   */
  public void testPowerSetHashCode_inputHashCodeTimesTooFarValueIsZero() {

      Maps.capacity(-1);
      fail("Negative expected size must result in IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  /**
   * Tests that nHMWES makes hash maps large enough that adding the expected number of elements
   * won't cause a rehash.
   *
   * <p>As of jdk7u40, HashMap has an empty-map optimization. The argument to new HashMap(int) is

      Maps.capacity(-1);
      fail("Negative expected size must result in IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  /**
   * Tests that nHMWES makes hash maps large enough that adding the expected number of elements
   * won't cause a rehash.
   *
   * <p>As of jdk7u40, HashMap has an empty-map optimization. The argument to new HashMap(int) is

    if (key == null) {
      return null;
    }
    int hash = hash(key);
    return segmentFor(hash).getEntry(key, hash);
  }

  @Override
  public boolean containsKey(@CheckForNull Object key) {
    if (key == null) {
      return false;
    }
    int hash = hash(key);
    return segmentFor(hash).containsKey(key, hash);
  }

  @Override

        adjust = ~~adjust;
        // in GWT, we have to deal with integer overflow carefully
      }
      int hash = 1;
      for (Set<E> axis : axes) {
        hash = 31 * hash + (size() / axis.size() * axis.hashCode());

        hash = ~~hash;
      }
      hash += adjust;
      return ~~hash;
    }
  }

  /**
   * Returns the set of all possible subsets of {@code set}. For example, {@code

   *
   * <p>This implementation tries to be smart in a number of ways. It recognizes cases where the
   * negation is cheaper to precompute than the matcher itself; it tries to build small hash tables
   * for matchers that only match a few characters, and so on. In the worst-case scenario, it
   * constructs an eight-kilobyte bit array and queries that. In many situations this produces a

   *
   * <p>This implementation tries to be smart in a number of ways. It recognizes cases where the
   * negation is cheaper to precompute than the matcher itself; it tries to build small hash tables
   * for matchers that only match a few characters, and so on. In the worst-case scenario, it
   * constructs an eight-kilobyte bit array and queries that. In many situations this produces a

  }

  /**
   * Sets the minimum total size for the internal hash tables. For example, if the initial capacity
   * is {@code 60}, and the concurrency level is {@code 8}, then eight segments are created, each
   * having a hash table of size eight. Providing a large enough estimate at construction time

      }

      @Override
      @CheckForNull
      K getSuperclass(K type) {
        return delegate.getSuperclass(type);
      }
    }
  }

  // This happens to be the hash of the class as of now. So setting it makes a backward compatible
  // change. Going forward, if any incompatible change is added, we can change the UID back to 1.
  private static final long serialVersionUID = 3637540370352322684L;