#include<cstdio>
#include<cstring>
#include<string>
#include<queue>
#include<map>
#include<iostream>
#include<vector>
#include<cstdlib>
#include<cmath>
#include<stack>
#include<ctime>
#include<cctype>
#include<set>
#include<algorithm>
using namespace std;
const int INF=1e9+7;
typedef pair<int,int> pii;
typedef long long ll;
int a[50010];
ll ans[50010],cnt;
int main(){
//    freopen("D://input.txt","r",stdin);
    int T;scanf("%d",&T);
    while(T--){
        int n;scanf("%d",&n);
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
        }
        sort(a+1,a+n+1);
        cnt=a[1];
        for(int i=1;i<=n;i++)
        {
            ans[i]=cnt;
            cnt=max(cnt,a[i+1]-ans[i]);
        }
        printf("%I64d\n",ans[n]);
    }
//  printf("%.3f\n",(double)clock()/CLOCKS_PER_SEC);
    return 0;
}