#include <bits/stdc++.h>
using namespace std;
const int N = 100010;
int n, k, a[N];
int ch[N * 31][2], cnt[N * 31], tot;
int ans, sum;

void insert(int x, int w) {
    int u = 1; cnt[u] += w;
    for(int i = 30; ~i; i--) {
        int c = (x >> i) & 1;
        if(!ch[u][c]) ch[u][c] = ++tot;
        u = ch[u][c], cnt[u] += w;
    }
}
int ask(int x) {
    int res = 0, u = 1;
    for(int i = 30; ~i; i--) {
        int c = (x >> i) & 1;
        if(ch[u][c] && cnt[ch[u][c]]) u = ch[u][c];
        else u = ch[u][c ^ 1], res += (1 << i);
    }
    return res;
}
void solve() {
    cin >> n >> k;
    ans = 0;
    for(int i = 1; i <= n; i++) cin >> a[i], ans ^= a[i];
    sum = ans; ans = 0;
    if(n == 1) {
        cout << ans << "\n"; return ;
    }
    for(int i = 1; i <= tot; i++) {
        memset(ch[i], 0, sizeof(ch[i]));
        cnt[i] = 0;
    }
    tot = 1;
    for(int i = 1; i <= n; i++) {
        if(a[i] > 0) {
            insert(a[i] ^ (a[i] - 1), 1);
        }
    }
    for(int i = 1; i <= n; i++) {
        if(a[i] > 0) {
            insert(a[i] ^ (a[i] - 1), -1);
        }
        insert(a[i] ^ (a[i] + 1), 1);
        ans = max(ans, ask(sum ^ a[i] ^ (a[i] + 1)));
        insert(a[i] ^ (a[i] + 1), -1);
        // cout << "### " << i << " : " << ask(sum ^ a[i] ^ (a[i] + 1)) << "\n";
        if(a[i] > 0) {
            insert(a[i] ^ (a[i] - 1), 1);
        }
    }
    cout << ans << "\n";
}
int main() {
    ios::sync_with_stdio(0); cin.tie(nullptr);
    int T; cin >> T;
    for(; T; --T) solve();
    return 0;
}