#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t;
    cin >> t;
    while(t--){
        int n,k;
        cin >> n >> k;
        vector<ll> a[2];
        int tot = 0;
        rep(i,n){
            ll x;
            cin >> x;
            a[x>=k].emplace_back(x%k);
            tot += x%k;
        }
        if(tot%k){
            cout << "-1\n";
            continue;
        }
        if(!tot){
            cout << "0\n";
            continue;
        }
        int l = -1, r = a[1].size()+1, ans = -1;
        while(l+1<r){
            int md = (l+r)/2, cnt = 0;
            priority_queue<int> pq;
            for(int x:a[0]) pq.emplace(x);
            rep(i,a[1].size()) pq.emplace(a[1][i]+k*(i<md));
            bool f = true;
            while(f && pq.top()>0){
                ++cnt;
                vector<int> v;
                rep(i,k){
                    if(!pq.top()){
                        f = false;
                        break;
                    }
                    v.emplace_back(pq.top()-1);
                    pq.pop();
                }
                for(int x:v) pq.emplace(x);
            }
            if(f) r = md, ans = cnt;
            else l = md;
        }
        cout << ans << '\n';
    }
    return 0;
}