#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=2e5+10;
ll T,n,k,L,a[N],d[N],ans=0,maxd=-999,id=0,d0=0,dn=0;
bool check(int x,int t)
{
    ll cnt=0,kk=k;
    d[n]=dn,d[0]=d0;
    maxd=max(max(d[0],d[n]),d[n-t]);
    while(x--){
        kk--,t++;
        d[0]+=maxd/2,d[n]+=maxd/2;
        cnt+=maxd/2;
        maxd=d[n-t];
    }
    cnt=cnt+max(d[0],d[n])+(kk-1)*(d[0]+d[n]);
    if(cnt<=ans) return false;
    else{
        ans=cnt;
        return true;
    }
}
int main()
{
    freopen("fly.in","r",stdin);
    freopen("fly.out","w",stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    cin>>T;
    while(T--){
        cin>>n>>k>>L;
        for(int i=1;i<=n;i++) cin>>a[i];
        sort(a+1,a+n+1);
        d[0]=a[1],d[n]=L-a[n];
        for(int i=1;i<n;i++) d[i]=a[i+1]-a[i];
        sort(d+1,d+n);
        ans=0;
        d0=d[0],dn=d[n];
        int l=0,r=min(k,n-1);
        check(l,1),check(r,1);
        while(l<=r&&r<=min(k,n)){
            int mid=l+r>>1;
            if(check(mid,1)) r=mid-1;
            else l=mid+1;
        }
        cout<<ans<<endl;
    }
    return 0;
}