#include <iostream>
#include <cmath>
#include <vector>
#include <cctype>
#include <cassert>
#include <random>
#include <map>

#define ld long double 
#define pb push_back
#define all(a) a.begin(), a.end()

using namespace std;

const int INF = 1e9;

int main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
#endif
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t--) {
        int n, k;
        cin >> n >> k;

        vector<int> a(n);

        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }

        int base_res = 0;

        for (int i = 0; i < n; i++) {
            base_res ^= a[i];
        }

        int ans = 0;

        vector<int> cnt(30);
        for (int i = 0; i < n; i++) {
            if (a[i] != 0) {
                cnt[__builtin_ctz(a[i])]++;
            }
        }

        for (int i = 0; i < n; i++) {
            int res = base_res ^ a[i] ^ (a[i] + 1);

            if (a[i] != 0) cnt[__builtin_ctz(a[i])]--;
            cnt[__builtin_ctz(a[i] + 1)]++;

            int best_result = INF;

            for (int j = 0; j < 30; j++) {
                if (cnt[j] > 0) {
                    best_result = min(best_result, res ^ ((1 << (j + 1)) - 1));
                }
            }

            ans = max(ans, best_result);

            if (a[i] != 0) cnt[__builtin_ctz(a[i])]++;
            cnt[__builtin_ctz(a[i] + 1)]--;
        }

        cout << ans << endl;
    }
    return 0;
}