public FluentBackoff withMaxBackoff(Duration maxBackoff) {
    checkArgument(
        maxBackoff.getMillis() > 0, "maxBackoff %s must be at least 1 millisecond", maxBackoff);
    return new FluentBackoff(
        exponent,
        initialBackoff,
        maxBackoff,
        maxCumulativeBackoff,
        maxRetries,
        throttledTimeCounter);
  }
@Test
  public void testInvalidMaxBackoff() {
    thrown.expect(IllegalArgumentException.class);
    thrown.expectMessage("maxBackoff PT0S must be at least 1 millisecond");
    defaultBackoff.withMaxBackoff(Duration.ZERO);
  }