#include <algorithm>
#include <cstdio>
//#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define SZ(x) ((int)(x).size())
#define fi first
#define se second
typedef long long ll;
typedef pair<int,int> PII;
const ll mod=1000000007;
ll powmod(ll a,ll b) {ll res=1;a%=mod;for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
// head

const int N=101000;
int _,n,c[N],dp[N];
int main() {
    for (scanf("%d",&_);_;_--) {
        scanf("%d",&n);
        rep(i,1,n+1) scanf("%d",c+i);
        int mv=0;
        sort(c+1,c+n+1);
        rep(i,1,n+1) {
            dp[i]=c[i]-mv;
            mv=max(mv,dp[i]);
        }
        printf("%d\n",mv);
    }
}