// Problem: A. 【PR #12】电塔
// URL: https://pjudge.ac/contest/1526/problem/21807
// Writer: WRuperD
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}return x*f;}
inline void write(int x){if(x<0){x=~(x-1);putchar('-');}if(x>9)write(x/10);putchar(x%10+'0');}
#define put() putchar(' ')
#define endl puts("")
const int MAX = 1e6 + 10;
int a[MAX];
void solve(){
	int n = read(), d = read();
	for(int i = 1; i <= n; i++)	a[i] = read();
	sort(a + 1, a + n + 1);
	for(int i = 1; i <= n; i++)	a[i] -= d * (i - 1);
	priority_queue <int> q;
	int ans = 0;
	for(int i = 1; i <= n; i++){
		int x = a[i];
		q.push(x);
		if(x <= q.top()){
			ans += q.top() - x;
			q.pop();
			q.push(x > 0 ? x : 0);
		}
	}
	write(ans), endl;
}
 
signed main(){
	int t = read();
	while(t--)	solve();
	return 0;
}