#pragma comment(linker,"/STACK:102400000,102400000")
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <cassert>
#include <climits>
#include <ctime>
#include <numeric>
#include <vector>
#include <algorithm>
#include <bitset>
#include <math.h>
#include <string.h>
#include <iomanip>
#include <complex>
#include <deque>
#include <functional>
#include <list>
#include <map>
#include <string>
#include <sstream>
#include <set>
#include <stack>
#include <queue>
using namespace std;
template<class T> inline T sqr(T x)
{
    return x * x;
}
typedef long long LL;
typedef unsigned long long ULL;
typedef long double db;
typedef pair<int, int> PII;
typedef pair<PII, int> PIII;
typedef pair<LL, LL> PLL;
typedef pair<LL, int> PLI;
typedef pair<db, db> PDD;
#define MP make_pair
#define PB push_back
#define sz(x) ((int)(x).size())
#define mem(ar,val) memset(ar, val, sizeof(ar))
#define istr stringstream
#define FOR(i,n) for(int i=0;i<(n);++i)
#define forIt(mp,it) for(__typeof(mp.begin()) it = mp.begin();it!=mp.end();it++)
const double EPS = 1e-6;
const int INF = 0x3fffffff;
const LL LINF = INF * 1ll * INF;
const double PI = acos(-1.0);
const int maxn= 1e6+10;

#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define lowbit(u) (u&(-u))

using namespace std;
#define lowbit(a) a&-a

int dir4[4][2]= {{1,0},{0,1},{-1,0},{0,-1}};
int dir8[8][2]= {{1,0},{1,1},{0,1},{-1,1},{-1,0},{-1,-1},{0,-1},{1,-1}};
int dir6[6][3]= {{0,0,1},{0,0,-1},{0,1,0},{0,-1,0},{1,0,0},{-1,0,0}};///六个方向
int movv[5][2]= {{1,0},{0,1},{0,0},{-1,0},{0,-1}};

inline LL read()
{
    int c=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-')f=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')
    {
        c=c*10+ch-'0';
        ch=getchar();
    }
    return c*f;
}
int a[maxn],b[maxn];
int main()
{
    int t ;t=read();
    while(t--)
    {
        int n,maxx=0; n=read();
        for (int i=1; i<=n; i++)  a[i]=read();
        sort(a+1,a+n+1);
        for (int i=1; i<=n; i++)  maxx=max(maxx,a[i]-b[i-1]),b[i]=maxx;
        printf("%d\n",b[n]);
    }
    return 0;
}