//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
void solve()
{
	int n;
	cin>>n;
	vector<int> vec(n);
	for(auto &x:vec) cin>>x;
	int ans=0;
	for(int d=29;d>=0;d--)
	{
		for(auto &x:vec) x&=((1<<(d+1))-1);
		srt(vec);
		uni(vec);
		int cnt0=0;
		for(auto x:vec) if(!(x>>d&1)) cnt0++;
		if(cnt0==(1<<d))
		{
			ans=(1<<(d+1))-1;
			break;
			vector<int> nvec;
			for(auto x:vec)
				if(x>>d&1)
					nvec.pb(x);
			swap(vec,nvec);
		}
	}
	cout<<ans<<'\n';
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t;
	cin>>t;
	while(t--)
		solve();
	return 0;
}