#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define N 10000000001
inline ll read(){
	ll x=0,f=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-')f=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		x=x*10+c-'0';
		c=getchar();
	}
	return x*f;
}
ll maxz,lst_maxz,minz;
ll T,n,a;
int main(){
	freopen("MOD.in","r",stdin);
	freopen("MOD.out","w",stdout);
	T=read();
	while(T--){
		maxz=0,lst_maxz=0,minz=N;
		n=read();
		for(int i=1;i<=n;i++){
			a=read();
			minz=min(minz,a);
			if(a>maxz){
				lst_maxz=maxz;
				maxz=a;
			}else if(a>lst_maxz&&a<maxz){
				lst_maxz=a;
			}
		}
		if(n==1){
			cout<<"0\n";
			continue;
		}
		cout<<max(maxz-minz,lst_maxz)<<endl;
	}
//	return 0;
	return 0;
}