public int attempts() {
    return this.attempts.intValue();
  }
@Test
  void attempts() {
    final var e = new BusinessException("unhandled");
    final var retry = new RetryExponentialBackoff<String>(
        () -> {
          throw e;
        },
        2,
        0
    );
    try {
      retry.perform();
    } catch (BusinessException ex) {
      //ignore
    }

    assertThat(retry.attempts(), is(1));
  }