fn main() {
    let mut t = String::new();
    std::io::stdin().read_line(&mut t).ok();
    let t: usize = t.trim().parse().unwrap();
    for _ in 0..t {
        let mut nl = String::new();
        std::io::stdin().read_line(&mut nl).ok();
        let nl: Vec<usize> = nl.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        let n = nl[0];
        let l = nl[1];
        let points = (0..n).map(|_| {
                let mut temmp = String::new();
                std::io::stdin().read_line(&mut temmp).ok();
                let temmp: Vec<usize> = temmp.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
                (temmp[0], temmp[1])
            })
            .collect::<Vec<_>>();

        let unit = (l as f64 / (n as f64).sqrt()).ceil() as usize;
        let size = l / unit + if l % unit > 0 { 1 } else { 0 };
        let mut blocks = vec![vec![]; size];
        for &(x, y) in points.iter() {
            blocks[y/unit].push((x, y));
        }
        for i in 0..size {
            blocks[i].sort();
        }
        let mut result = Vec::with_capacity(n);
        let mut rev = false;
        for i in 0..size {
            if blocks[i].is_empty() { continue; }
            if rev {
                for &p in blocks[i].iter().rev() {
                    result.push(p);
                }
            } else {
                for &p in blocks[i].iter() {
                    result.push(p);
                }
            }
            rev = !rev;
        }
        println!("{n}");
        let result = result.into_iter().map(|p| format!("{} {}", p.0, p.1)).collect::<Vec<_>>();
        println!("{}", result.join("\n"));
    }
}