#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
#include<algorithm>
#include<string>
#include<set>

using namespace std;
long long a[100000];
set <long long> set1;
int main()
{
    long long n,m,T,i,j;
    cin >> T;
    while (T--){
        cin >> n;
        set1.clear();
        for (i=1;i<=n;i++) {
            scanf("%I64d",&a[i]);
            set1.insert(a[i]);
        }
        copy(set1.begin(),set1.end(),a);
        n=set1.size();
        long long ans=0;
        for (int i=0;i<n;i++){
            ans=max(ans,a[i]-ans);
        }
        cout << ans << endl;
    }
}