#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll t,n,a[100010];
int main () {
	freopen("mod.in","r",stdin);
	freopen("mod.out","w",stdout);
	cin >> t;
	while (t--) {
		ll mx=0;
		cin >> n;
		for (int i=1;i<=n;i++) {
			cin >> a[i];
			mx=max(mx,a[i]);
		}
		ll res=0,minn=1e9+10,maxx=0; 
		for (int i=1;i<=n;i++) {
			maxx=max(maxx,a[i]%mx);
			minn=min(minn,a[i]%mx);
		}
		res=max(res,maxx-minn);
		minn=1e9+10,maxx=0; 
		for (int i=1;i<=n;i++) {
			maxx=max(maxx,a[i]%(mx+1));
			minn=min(minn,a[i]%(mx+1));
		}
		res=max(res,maxx-minn);
		cout << res <<endl;
	}
	return 0;
}