private static GetCheckedTypeValidator bestGetCheckedTypeValidator() {
    return GetCheckedTypeValidatorHolder.BEST_VALIDATOR;
  }

  @VisibleForTesting
  static GetCheckedTypeValidator weakSetValidator() {
    return GetCheckedTypeValidatorHolder.WeakSetValidator.INSTANCE;
  }

  /**
   * Provides a check of whether an exception type is valid for use with {@link
   * FuturesGetChecked#getChecked(Future, Class)}, possibly using caching.

    return new WeakReference<>(shadowLoader);
  }

  /*
   * TODO(cpovirk): It would be great to run all these tests (including class unloading) in an
   * environment that forces Futures.getChecked to its fallback WeakSetValidator. One awful way of
   * doing so would be to derive a separate test library by using remove_from_jar to strip out
   * ClassValueValidator.
   *

    return new WeakReference<>(shadowLoader);
  }

  /*
   * TODO(cpovirk): It would be great to run all these tests (including class unloading) in an
   * environment that forces Futures.getChecked to its fallback WeakSetValidator. One awful way of
   * doing so would be to derive a separate test library by using remove_from_jar to strip out
   * ClassValueValidator.
   *