static int parseInt(String key, @Nullable String value) {
    requireArgument((value != null) && !value.isEmpty(), "value of key %s was omitted", key);
    try {
      return Integer.parseInt(value);
    } catch (NumberFormatException e) {
      throw new IllegalArgumentException(String.format(US,
          "key %s value was set to %s, must be an integer", key, value), e);
    }
  }
@Test
  public void parseInt_exception() {
    assertThrows(IllegalArgumentException.class, () -> CaffeineSpec.parseInt("key", "value"));
  }