private final ClassSanityTester tester = new ClassSanityTester();
  private Visibility visibility = Visibility.PACKAGE;
  private Predicate<Class<?>> classFilter =
      (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;