#include<bits/stdc++.h>
using namespace std;
long long T,n,a[200005],mx,mx1,mn;
int main(){
    freopen("mod.in","r",stdin);
    freopen("mod.out","w",stdout);
    scanf("%lld",&T);
    while(T--){
        scanf("%lld",&n);
        mx=mx1=-1,mn=100000000000;
        for(int i=1;i<=n;i++){
            scanf("%lld",&a[i]);
            if(a[i]>=mx) mx=a[i];
            else mx1=max(mx1,a[i]);
            mn=min(mn,a[i]);
        }
        printf("%lld\n",max(mx-mn,mx1));
    }
	return 0;
}
/*
3
1
1
4
2 0 2 4
8
3 1 4 1 5 9 2 6
*/