#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#include<map>
#include<cmath>
#include<deque>
#include<functional>
#include<iterator>
#include<set>
#include<utility>
#include<stack>
#include<queue>
#include<bitset>
using namespace std;
#define maxn 300000
#define inf 1500000007
const int mod = 1e9+7;
using namespace std; //  0 0 0 0
int a[maxn];
long long dp[maxn],ma;
int main()
{
    int T,n,i,j,k;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(i=1;i<=n;++i)
            scanf("%d",&a[i]);
        sort(a+1,a+1+n);
        ma = a[1];
        for(i=1;i<=n;++i)
        {
            dp[i] = ma;
            ma = max(ma,a[i+1] - dp[i]);
        }
        printf("%I64d\n",dp[n]);
    }
    return 0;
}