#include<bits/stdc++.h>
using namespace std;
#define int long long
int n,a[1000005];
int T;
signed main(){
    freopen("mod.in","r",stdin);
    freopen("mod.out","w",stdout);
    cin.tie(0),cout.tie(0);
    cin>>T;
    while(T--){
	    cin>>n;
	    for(int i=1;i<=n;i++){
	    	cin>>a[i];
	    }
	    int minnn=5e18,maxxn=0;
	    for(int i=1;i<=n;i++){
	    	minnn=min(minnn,a[i]);
	    	maxxn=max(maxxn,a[i]);
	    }
	    int minn=5e18,maxn=0;
	    for(int i=1;i<=n;i++){
	    	maxn=max(maxn,a[i]);
	    }
	    for(int i=1;i<=n;i++){
	    	a[i]%=maxn;
	    }
		minn=5e18,maxn=0;
	    for(int i=1;i<=n;i++){
	    	minn=min(minn,a[i]);
	    	maxn=max(maxn,a[i]);
	    }
	    cout<<max(maxn-minn,maxxn-minnn)<<'\n';
    }
    
    return 0;
}