#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


int N;
Int K;
vector<Int> A;

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%d%lld", &N, &K);
    A.resize(N);
    for (int i = 0; i < N; ++i) {
      scanf("%lld", &A[i]);
    }
    
    Int base = 0;
    for (int i = 0; i < N; ++i) {
      base ^= A[i];
    }
    
    multiset<Int> ds;
    for (int i = 0; i < N; ++i) {
      if (A[i] > 0) ds.insert(A[i] ^ (A[i] - 1));
    }
    
    Int mx = -1;
    for (int i = 0; i < N; ++i) {
      if (A[i] > 0) ds.erase(ds.find(A[i] ^ (A[i] - 1)));
      Int mn = base;
      for (const Int d : ds) {
        Int t = base;
        t ^= A[i] ^ (A[i] + 1);
        t ^= d;
        chmin(mn, t);
      }
      chmax(mx, mn);
      if (A[i] > 0) ds.insert(A[i] ^ (A[i] - 1));
    }
    printf("%lld\n", mx);
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}