#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <atcoder/modint>
using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(int)(n); i++)


const i64 INF = 1001001001001001001;
using modint = atcoder::static_modint<998244353>;


void testcase(){
    int N; cin >> N;
    u64 Y; cin >> Y;
    vector<u64> A(N); rep(i,N) cin >> A[i];
    vector<u64> B = A;
    const u64 IMPOSSIBLE = ~(u64)0;
    vector<u64> dp = {0};
    rep(d,61){
        u64 lowerBit1 = ((u64)1 << d) - 1;
        u64 lowerBit = ((u64)1 << (d + 1)) - 1;
        auto cmpByLowerBit1 = [lowerBit1](u64 l, u64 r) -> bool { return (l & lowerBit1) < (r & lowerBit1); };
        auto cmpByLowerBit = [lowerBit](u64 l, u64 r) -> bool { return (l & lowerBit) < (r & lowerBit); };
        sort(A.begin(), A.end(), cmpByLowerBit1);
        sort(B.begin(), B.end(), cmpByLowerBit);
        vector<u64> tmp(N + 1, IMPOSSIBLE);

        int rawcnt = 0;
        for(u64 a : A) if(a & ((u64)1 << d)) rawcnt ^= 1;
        int tgcnt = (Y >> d) & 1;

        for(u64 x : dp){
            int p = A.end() - lower_bound(A.begin(), A.end(), ((u64)1 << d) - x, cmpByLowerBit1);
            if(x == 0) p = 0;
            rep(t,2) if(d != 60 || t == 0){
                u64 nx = x | ((u64)t << d);
                int q = p & 1;
                if((rawcnt ^ q ^ ((t*N)&1)) != tgcnt) continue;

                int pp = B.end() - lower_bound(B.begin(), B.end(), ((u64)1 << (d + 1)) - nx, cmpByLowerBit);
                if(nx == 0) pp = 0;
                tmp[pp] = min(tmp[pp], nx);
            }
        }

        dp.clear();
        for(u64 x : tmp) if(x != IMPOSSIBLE) dp.push_back(x);

    }

    u64 ans = IMPOSSIBLE;
    for(auto a : dp) ans = min(ans, a);
    cout << (i64)ans << '\n';

}


int main(){
    int T; cin >> T;
    while(T --> 0) testcase();
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(nullptr);
    }
} ios_do_not_sync_instance;