from collections import Counter
for _ in range(int(input())):
n,k=map(int,input().split())
arr=list(map(int,input().split()))
d=Counter()
for i in arr:
if i%k!=0:
d[k-i%k]+=1
ma=0
for i in d:
ma=max(ma,i+d[i]*k-k+1)
print(ma)
#include<bits/stdc++.h>
using namespace std ;
#define ll long long
int main(){
int t; cin>>t ;
while(t--){
ll n,k ; cin>>n>>k ;
ll arr[n] ;
for(int i=0; i<n; i++) {
cin>>arr[i] ;
arr[i] = k - arr[i]%k ;
if(arr[i]==k){
arr[i]=0 ;
}
}
sort(arr,arr+n) ;
ll ans = 0 ;
map<ll,ll>mp ;
for(int i=0; i<n; i++){
if(arr[i]!=0 && mp[arr[i]]==0){
mp[arr[i]] = arr[i] ;
ans = max(ans,arr[i]) ;
}
else if(arr[i]!=0 && mp[arr[i]]!=0){
ans = max(ans,k+mp[arr[i]]) ;
mp[arr[i]] += k ;
}
}
if(ans==0){
ans=-1 ;
}
cout<<ans+1<<endl;
}
}
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