try {
      tester.test();
    } catch (AssertionError expected) {
      return;
    }
    fail();
  }

  private static final class ThrowingIterator<E> implements Iterator<E> {
    private final RuntimeException ex;

    private ThrowingIterator(RuntimeException ex) {
      this.ex = ex;
    }

    @Override
    public boolean hasNext() {