#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int q; cin >> q;
    while (q--) {
        int n,k; cin >> n >> k;
        vector<int> a(n);
        int x = 0;
        for (int i = 0; i < n; ++i) {
            cin >> a[i];
            x ^= a[i];
        }
        int res = -1;
        vector<vector<pair<int,int>>> v(40);
        for (int i = 0; i < n; ++i) {
            int cnt = 0;
            for (int j = 0; j < 30; ++j) {
                if ((1LL<<j)&a[i]) break;
                cnt += 1;
            }
            if (v[cnt].size() < 2) v[cnt].emplace_back(a[i], i);
        }
        vector<pair<int,int>> b;
        for (int i = 0; i < 40; ++i) {
            for (auto p : v[i]) b.push_back(p);
        }
        for (int i = 0; i < n; ++i) {
            int y = (x ^ a[i] ^ (a[i]+1));
            int mi = x;
            for (auto p : b) {
                if (p.second == i) continue;
                if (p.first > 0) mi = min(mi, y^p.first^(p.first-1));
            }
            res = max(res, mi);
        }
        cout << res << "\n";
    }
}