#include <bits/stdc++.h>
using namespace std;
const int N=200010;
int t,n,a[N],b[N],c[N];
int main() {
	freopen("mod.in","r",stdin);
	freopen("mod.out","w",stdout);
	cin>>t;
	while (t--)
	{
		scanf("%d",&n);
		for (int i=1;i<=n;i++)
		{
			scanf("%d",&a[i]);
		}
		int mx=0;
		for (int i=1;i<=n;i++)
		{
			mx=max(mx,a[i]);
		}
		int bmx=0,bmi=1e9+10,cmx=0,cmi=1e9+10;
		for (int i=1;i<=n;i++)
		{
			b[i]=a[i]%mx;
			c[i]=a[i]%(mx+1);
			bmx=max(bmx,b[i]);
			bmi=min(bmi,b[i]);
			cmx=max(cmx,c[i]);
			cmi=min(cmi,c[i]);
		}
		printf("%d\n",max(bmx-bmi,cmx-cmi));
	}
}