You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cubic.rs
    path of file: ./repos/tquic/src/congestion_control
    
    the code of the file until where you have to start completion: // Copyright (c) 2023 The TQUIC Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::sync::Arc;
use std::time::Duration;
use std::time::Instant;

use log::*;

use super::CongestionController;
use super::CongestionStats;
use super::HystartPlusPlus;
use crate::connection::rtt::RttEstimator;
use crate::connection::s
    
    fn cubic_ack() {
        let cubic_cfg = CubicConfig::default();
        let mut cubic = Cubic::new(cubic_cfg);
        let now = Instant::now();
        let mut pkts: Vec<SentPacket> = Vec::new(); // let mut pkts_part3: Vec<SentPacket> = Vec::new();
        let rtt = RttEstimator::new(Duration::from_millis(20));
        let bytes_lost = 0;
        let pkt_size: u64 = 240;
        let n_pkts = 6;

        // Packets for sample 1.
        for n in 0..n_pkts {
            pkts.push(SentPacket {
                pkt_num: n,
                frames: Vec::new(),
                // Sent timestamp differs.
                time_sent: now + Duration::from_millis(n),
                time_acked: Some(now + Duration::from_millis(20)),
                time_lost: None,
                ack_eliciting: true,
                in_flight: true,
                has_data: false,
                sent_size: pkt_size as usize,
                rate_sample_state: Default::default(),
                ..SentPacket::default()
            });
        }

        // In slow start.
        let mut time_acked = now + Duration::from_millis(20);
        let mut cwnd = cubic.congestion_window();
        cubic.begin_ack(time_acked, pkt_size);
        for i in 0..(n_pkts - 3) {
            cubic.on_ack(&mut pkts[i as usize], time_acked, false, &rtt, 0);
        }
        cubic.end_ack();
        assert_eq!(cubic.hystart.has_exited(), false);
        assert_eq!(cubic.in_slow_start(), true);
        assert_eq!(cubic.congestion_window(), cwnd + (n_pkts - 3) * pkt_size);

        // Congestion event.
        cwnd = cubic.congestion_window();
        cubic.on_congestion_event(time_acked, &pkts[(n_pkts - 3) as usize], false, pkt_size, 0);
        assert_eq!(cubic.w_max, cwnd as f64);
        assert_eq!(cubic.ssthresh, (cwnd as f64 * cubic.config.beta) as u64);
        assert_eq!(cubic.cwnd, cubic.ssthresh);

        cwnd = cubic.congestion_window();
        pkts[(n_pkts - 2) as usize].time_sent = time_acked + Duration::from_millis(5);
        cubic.on_congestion_event(
            time_acked + Duration::from_millis(20),
            &pkts[(n_pkts - 2) as usize],
            false,
            pkt_size,
            0,
        );
        assert_eq!(cubic.w_max, cwnd as f64 * (1.0 + cubic.config.beta) / 2.0);
        assert_eq!(cubic.ssthresh, (cwnd as f64 * cubic.config.beta) as u64);
        assert_eq!(cubic.cwnd, cubic.ssthresh);

        // In congestion avoidance.
        assert_eq!(cubic.in_slow_start(), false);
        assert_eq!(cubic.hystart.has_exited(), true);
        pkts[(n_pkts - 1) as usize].time_sent = time_acked + Duration::from_millis(25);
        time_acked += Duration::from_millis(30);
        cubic.begin_ack(time_acked, 0);
        cubic.on_ack(&mut pkts[(n_pkts - 1) as usize], time_acked, false, &rtt, 0);
        cubic.end_ack();
        assert!(cubic.cwnd >= cubic.ssthresh);
    }