(Class<?> cls) -> visibility.isVisible(cls.getModifiers());

  /**
   * Restricts the sanity tests for public API only. By default, package-private API are also
   * covered.
   */
  protected final void publicApiOnly() {
    visibility = Visibility.PUBLIC;
  }

  /**
   * Tests all top-level {@link Serializable} classes in the package. For a serializable Class
   * {@code C}:
   *
   * <ul>