#include <cstdio>
#include <algorithm>
#define LL  long long
//------------------------------------------------------------
void Max(LL &num1,LL num2) { if (num1<num2) num1=num2; }
void Min(LL &num1,LL num2) { if (num1>num2) num1=num2; }
//------------------------------------------------------------
int  tcase;
int  icase;

int  n;
int  i,j;
LL   v[100000];


LL   max[100000];
LL   min[100000];
//------------------------------------------------------------
int  main( )
{
    for (scanf("%d",&tcase); ++icase<=tcase; )
    {
        //--0 init
        scanf("%d",&n);
        for (i=1; i<=n; i++) scanf("%I64d",&v[i]);
        std::sort(v+1,v+1+n);
        
        //--1
        for (i=1; i<=n; i++)
        {
            max[i]=max[i-1];
            Max(max[i],v[i]-max[i-1]);
//            min[i]=min[i-1];
//            Min(min[i],v[i]-max[i-1]);
        }
        
        //--2
        printf("%I64d\n",max[n]);
    }
}