*     string using {@link String#valueOf(Object)}
   * @throws IllegalArgumentException if {@code expression} is false
   */
  public static void checkArgument(boolean expression, @CheckForNull Object errorMessage) {
    if (!expression) {
      throw new IllegalArgumentException(String.valueOf(errorMessage));
    }
  }

  /**

          .add(doubleConversionTest + i);
      BigInteger bigI = BigInteger.valueOf(i);
      testBigIntegersBuilder
          .add(bigI)
          .add(BigInteger.valueOf(Long.MAX_VALUE).add(bigI))
          .add(BigInteger.valueOf(Long.MIN_VALUE).add(bigI))
          .add(BigInteger.valueOf(Integer.MAX_VALUE).add(bigI))
          .add(BigInteger.valueOf(Integer.MIN_VALUE).add(bigI))
          .add(BigInteger.ONE.shiftLeft(63).add(bigI))

    assertFalse(Objects.equal("1", 1));
  }

  public void testHashCode() throws Exception {
    int h1 = Objects.hashCode(1, "two", 3.0);
    int h2 = Objects.hashCode(Integer.valueOf(1), new String("two"), Double.valueOf(3.0));
    // repeatable
    assertEquals(h1, h2);

    // These don't strictly need to be true, but they're nice properties.
    assertTrue(Objects.hashCode(1, 2, null) != Objects.hashCode(1, 2));

    assertEquals(Integer.valueOf(5), reserialize(Suppliers.ofInstance(5)).get());
    assertEquals(
        Integer.valueOf(5),
        reserialize(Suppliers.compose(Functions.identity(), Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5), reserialize(Suppliers.memoize(Suppliers.ofInstance(5))).get());
    assertEquals(
        Integer.valueOf(5),

    assertEquals(Integer.valueOf(5), reserialize(Suppliers.ofInstance(5)).get());
    assertEquals(
        Integer.valueOf(5),
        reserialize(Suppliers.compose(Functions.identity(), Suppliers.ofInstance(5))).get());
    assertEquals(Integer.valueOf(5), reserialize(Suppliers.memoize(Suppliers.ofInstance(5))).get());
    assertEquals(
        Integer.valueOf(5),

      BigInteger.valueOf(Integer.MAX_VALUE)
          .multiply(BigInteger.valueOf(3L))
          .divide(BigInteger.valueOf(4L))
          .doubleValue();
  static final double LARGE_INTEGER_VALUES_POPULATION_VARIANCE =
      BigInteger.valueOf(Integer.MAX_VALUE)
          .multiply(BigInteger.valueOf(Integer.MAX_VALUE))
          .divide(BigInteger.valueOf(16L))
          .doubleValue();

    new EqualsTester()
        .addEqualityGroup(Optional.absent(), reserialize(Optional.absent()))
        .addEqualityGroup(Optional.of(Long.valueOf(5)), reserialize(Optional.of(Long.valueOf(5))))
        .addEqualityGroup(Optional.of(Long.valueOf(42)), reserialize(Optional.of(Long.valueOf(42))))
        .testEquals();
  }

  public void testToString_absent() {
    assertEquals("Optional.absent()", Optional.absent().toString());

  public void testBadStrings() {
    UnicodeEscaper e = SIMPLE_ESCAPER;
    String[] BAD_STRINGS = {
      String.valueOf(Character.MIN_LOW_SURROGATE),
      Character.MIN_LOW_SURROGATE + "xyz",
      "abc" + Character.MIN_LOW_SURROGATE,
      "abc" + Character.MIN_LOW_SURROGATE + "xyz",
      String.valueOf(Character.MAX_LOW_SURROGATE),
      Character.MAX_LOW_SURROGATE + "xyz",
      "abc" + Character.MAX_LOW_SURROGATE,

        return (T) Character.valueOf('\0');
      } else if (type == byte.class) {
        return (T) Byte.valueOf((byte) 0);
      } else if (type == short.class) {
        return (T) Short.valueOf((short) 0);
      } else if (type == int.class) {
        return (T) Integer.valueOf(0);
      } else if (type == long.class) {
        return (T) Long.valueOf(0L);
      } else if (type == float.class) {

        for (; i < length; i++) {
          char c = chars[i];
          if (isUpperCase(c)) {
            chars[i] = (char) (c ^ CASE_MASK);
          }
        }
        return String.valueOf(chars);
      }
    }
    return string;
  }

  /**
   * Returns a copy of the input character sequence in which all {@linkplain #isUpperCase(char)