#include <bits/stdc++.h>

#define rep(i, j, k) for (int i = (j); i <= (k); ++i)
#define per(i, j, k) for (int i = (j); i >= (k); --i)
#define SZ(v) int((v).size())
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
using ll = long long;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;

template<class T> void chkmn(T &x, T y) { if (y < x) x = y; }
template<class T> void chkmx(T &x, T y) { if (y > x) x = y; }

using namespace std;

const int maxn = 100010;
const int maxm = maxn * 35;

int n, k, a[maxn], b[maxn], c[maxn], mn[maxn], son[maxm][2], tot;
vector<int> res;

void init() {
  rep (i, 1, tot) son[i][0] = son[i][1] = 0;
  tot = 1;
}

void ins(int x) {
  int p = 1;
  per (i, 30, 0) {
    if (!son[p][x >> i & 1]) son[p][x >> i & 1] = ++tot;
    p = son[p][x >> i & 1];
  }
}

int qry(int x) {
  int p = 1, ans = 0;
  per (i, 30, 0) {
    if (son[p][x >> i & 1]) p = son[p][x >> i & 1];
    else p = son[p][(x >> i & 1) ^ 1], ans |= (1 << i);
  }
  return ans;
}

void work() {
  cin >> n >> k;
  rep (i, 1, n) cin >> a[i];
  rep (i, 1, n) b[i] = a[i] ^ (a[i] + 1), c[i] = a[i] ^ (a[i] - 1);
  int s = 0;
  rep (i, 1, n) s ^= a[i];
  int ans = 0;
  rep (i, 1, n) mn[i] = s;
  init();
  rep (i, 1, n) {
    if (i != 1) chkmn(mn[i], qry(s ^ b[i]));
    ins(c[i]);
  }
  init();
  per (i, n, 1) {
    if (i != n) chkmn(mn[i], qry(s ^ b[i]));
    ins(c[i]);
  }
  rep (i, 1, n) {
    chkmx(ans, mn[i]);
  }
  cout << ans << '\n';
}

int main() {
  cin.tie(nullptr) -> ios::sync_with_stdio(false);
  int t; cin >> t;
  while (t--) work();
}