#include <bits/stdc++.h>
using namespace std;
#define ll long long
int gcd(int a,int b){
	return b ? gcd(b,a%b):a;
}
 
int main() {
	// your code goes here
	int t;
	cin>>t;
	vector<int> arr(200005);
	while(t--){
		int n,prev,data,start;
		cin>>n;
		if(n==1){
			cin>>data;
			cout<<0<<'\n';
			continue;
		}
		cin>>prev;
		start = prev;
		int max = prev;
		int min = prev;
		int ans = 0;
		for(int i=1;i<n;i++){
			cin>>data;
			int diff = prev-data;
			ans = ans>diff ? ans:diff;
			min = min<data ? min:data;
			max = max>data ? max:data;
			prev = data;
		}
		int diff = data-start;
		ans = ans>diff ? ans:diff;
		diff = max-start;
		ans = ans>diff ? ans:diff;
		diff = data-min;
		ans = ans>diff ? ans:diff;
 
		cout<<ans<<"\n";
	}
	return 0;
}

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NQo2CjEgMyA5IDExIDUgNwoxCjIwCjMKOSA5OSA5OTkKNAoyIDEgOCAxCjMKMiAxIDUK

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1
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3
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4
2 1 8 1
3
2 1 5