#include <iostream>
#include <algorithm>
#include <string>
#include <assert.h>
using namespace std;
 
 
 
long long readInt(long long l,long long r,char endd){
	long long x=0;
	int cnt=0;
	int fi=-1;
	bool is_neg=false;
	while(true){
		char g=getchar();
		if(g=='-'){
			assert(fi==-1);
			is_neg=true;
			continue;
		}
		if('0'<=g && g<='9'){
			x*=10;
			x+=g-'0';
			if(cnt==0){
				fi=g-'0';
			}
			cnt++;
			assert(fi!=0 || cnt==1);
			assert(fi!=0 || is_neg==false);
			
			assert(!(cnt>19 || ( cnt==19 && fi>1) ));
		} else if(g==endd){
			assert(cnt>0);
			if(is_neg){
				x= -x;
			}
			assert(l<=x && x<=r);
			return x;
		} else {
			assert(false);
		}
	}
}
string readString(int l,int r,char endd){
	string ret="";
	int cnt=0;
	while(true){
		char g=getchar();
		assert(g!=-1);
		if(g==endd){
			break;
		}
		cnt++;
		ret+=g;
	}
	assert(l<=cnt && cnt<=r);
	return ret;
}
long long readIntSp(long long l,long long r){
	return readInt(l,r,' ');
}
long long readIntLn(long long l,long long r){
	return readInt(l,r,'\n');
}
string readStringLn(int l,int r){
	return readString(l,r,'\n');
}
string readStringSp(int l,int r){
	return readString(l,r,' ');
}

int T;
int sm_n=0;
int n,m,k,l;
int arr[100100];
int main(){
	//freopen("00.txt","r",stdin);
	//freopen("00o.txt","w",stdout);
	T=readIntLn(1,1000);
	while(T--){
		n=readIntSp(1,100000);
		m=readIntSp(1,100000);
		k=readIntSp(1,1000000000);
		l=readIntLn(1,10000);
		for(int i=0;i<n;i++){
			if(i==n-1){
				arr[i]=readIntLn(1,k-1);
			} else {
				arr[i]=readIntSp(1,k-1);
			}
			
		}
		sort(arr,arr+n);
		arr[n++]=k;
		for(int i=2;i<=n;i++){
			assert(arr[i] != arr[i-1]);
		}
		int sol= (m+1) *l;
		int until = l;
		for(int i=0;i<n;i++){
			while(until <= arr[i] && m>0 && until <= k){
				m--;
				until += l;
			}
			if(m == 0){
				sol= min(sol,max(until - arr[i],0));
				break;
			}
			sol = min(sol, until-arr[i] + m *l);
			m++;
		}
		while(until <= k && m>0){
			until += l;
			m--;
		}
		cout<<sol<<endl;
	}
	assert(getchar()==-1);
}