#![allow(non_snake_case, unused_imports)]

use proconio::{input, marker::Usize1, marker::Chars};
use itertools::Itertools;

#[allow(unused_macros)]
macro_rules! d {
    ( $( $x:expr ),* $(,)? ) => {
        eprintln!(
            concat!( $( stringify!($x), "={:?} " ),* ),
            $( $x ),*
        );
    };
}

#[allow(dead_code)]
fn yn(b: bool) -> &'static str {
    if b { "Yes" } else { "No" }
}

fn main() {
    input! {
        T: usize,
    }

    for _ in 0..T {
        input! {
            N: usize,
            K: i64,
            A: [i64; N],
        }

        let slis = A.into_iter().sorted().collect_vec();
        let ans = match slis.as_slice() {
            [head, rest@..] => {
                rest.iter()
                    .copied()
                    .chain(std::iter::once(head - K))
                    .reduce(|a, b| a * b).unwrap()
            },
            &[] => unreachable!()
        };

        println!("{}", ans);
    }
}