#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

long long int t, n, m, k, l, a, ans1;
vector<long long int> V;

int main()
{
    cin>>t;
    
    for(int qq=1;qq<=t;qq++)
    {
        cin>>n>>m>>k>>l;
        V.clear();
        for(int i=1;i<=n;i++)
        {
            cin>>a;
            if(a>=k)
                continue;
            V.push_back(a);
        }
        
        sort(V.begin(), V.end());
        
        ans1 = (m+1)*l;
        
        for(int i=0;i<V.size();i++)
        {
            a = V[i]/l;
            if( (m+i+1)<= a)
            {
                ans1=0;
                break;
            }
            
            ans1 = min(ans1 , ((m+i+1)*l - V[i]) );
        }
        
        a = k/l;
        if((m+V.size()+1)<=a)
            ans1 = 0;
        else
            ans1 = min(ans1, (long long int)((m+V.size()+1)*l - k) );
        cout<<ans1<<"\n";
    }
}