#include<bits/stdc++.h>

#define endl '\n'
#define pii pair<int, int>
#define int long long
#define ld long double

using namespace std;

const int mod=1e9+7,M=2000010,Mlog=22;

void solve(){
    int n;
    cin>>n;

    vector<int>a(n+1),b(n+1,0),v;  
    map<int,vector<int>>m;
    set<int>s;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        m[a[i]].push_back(i);
        s.insert(a[i]);
    }

    for(int x:s){
        v.push_back(x);
    }

    reverse(v.begin(),v.end());


    if(m.size()==1){
        for(auto [x,_]:m){
            cout<<x<<endl;
            return;
        }
    }

    for(int i=1;i<=n;i++){
        b[i]=b[i-1]^a[i];
    }

    int ans=0;
    for(auto x:v){
        int ok=1;
        for(int i=0;i<m[x].size();i++){
            if(!i){
                if(b[m[x][i]-1]!=x&&m[x][i]!=1){
                    ok=0;
                    break;
                }
            } else{
                if(m[x][i]!=m[x][i-1]+1){
                    if(b[m[x][i]-1]^b[m[x][i-1]]!=x){
                        ok=0;
                        break;
                    }
                }
            }
        }
        if(m[x].back()!=n){
            if(b[n]^b[m[x].back()]!=x){
                ok=0;
            }
        }
        if(ok){
            ans=x;
            break;
        }
    }


    cout<<max(ans,b[n])<<endl;
}

signed main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int t;
    cin>>t;

    while(t--){
        solve();
    }



    return 0;
}