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: mod.rs
    path of file: ./repos/sled/tests/tree
    
    the code of the file until where you have to start completion: use std::{collections::BTreeMap, convert::TryInto, fmt, panic};

use quickcheck::{Arbitrary, Gen, RngCore};
use rand::{rngs::StdRng, Rng, SeedableRng};
use rand_distr::{Distribution, Gamma};

use sled::*;

#[derive(Clone, Ord, PartialOrd, Eq, PartialEq)]
pub struct Key(pub Vec<u8>);

impl fmt::Debug for Key {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if !self.0.is_empty() {
            write!(
                f,
                "Key(vec![{}; {}])",
                self.0.first().cop
    
    fn arbitrary<G: Gen>(g: &mut G) -> Self {
        if g.gen::<bool>() {
            let gs = g.size();
            let gamma = Gamma::new(0.3, gs as f64).unwrap();
            let v = gamma.sample(&mut rand::thread_rng());
            let len = if v > 3000.0 { 10000 } else { (v % 300.) as usize };

            let space = g.gen_range(0, gs) + 1;

            let inner = (0..len).map(|_| g.gen_range(0, space) as u8).collect();

            Self(inner)
        } else {
            let len = g.gen_range(0, 2);
            let mut inner = vec![];

            for _ in 0..len {
                inner.push(g.gen::<u8>());
            }

            Self(inner)
        }
    }