#define ll long long
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define mp make_pair
#define fo(i , n) for(ll i = 0 ; i < n ; i++)
//#include<bits/stdc++.h>
#include<iomanip>
#include<cmath>
#include<cstdio>
#include<utility>
#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<map>
#include<queue>
#include<set>
#include<stack>
ll pi = acos(-1) ;
ll z = 1000000007 ;
ll inf = 100000000000000000 ;
ll p1 = 37 ;
ll p2 = 53 ;
ll mod1 =  202976689 ;
ll mod2 =  203034253 ;
const int NN = 3e2 ;
ll fact[NN];
ll gdp(ll a , ll b){return (a - (a%b)) ;}
ll ld(ll a , ll b){if(a < 0) return -1*gdp(abs(a) , b) ; if(a%b == 0) return a ; return (a + (b - a%b)) ;} // least number >=a divisible by b
ll gd(ll a , ll b){if(a < 0) return(-1 * ld(abs(a) , b)) ;    return (a - (a%b)) ;} // greatest number <= a divisible by b
ll gcd(ll a , ll b){ if(b > a) return gcd(b , a) ; if(b == 0) return a ; return gcd(b , a%b) ;}
ll e_gcd(ll a , ll b , ll &x , ll &y){ if(b > a) return e_gcd(b , a , y , x) ; if(b == 0){x = 1 ; y = 0 ; return a ;}
ll x1 , y1 ; e_gcd(b , a%b , x1 , y1) ; x = y1 ; y = (x1 - ((a/b) * y1)) ; return e_gcd(b , a%b , x1 , y1) ;}
ll power(ll a ,ll b , ll p){if(b == 0) return 1 ; ll c = power(a , b/2 , p) ; if(b%2 == 0) return ((c*c)%p) ; else return ((((c*c)%p)*a)%p) ;}
ll inverse(ll a ,ll n){return power(a , n-2 , n) ;}
ll max(ll a , ll b){if(a > b) return a ; return b ;}
ll min(ll a , ll b){if(a < b) return a ; return b ;}
ll left(ll i){return ((2*i)+1) ;}
ll right(ll i){return ((2*i) + 2) ;}
ll ncr(ll n , ll r){if(n < r) return 0 ; return ((((fact[n] * inverse(fact[r] , z)) % z) * inverse(fact[n-r] , z)) % z);}
void swap(ll&a , ll&b){ll c = a ; a = b ; b = c ; return ;}
//ios_base::sync_with_stdio(0);
//cin.tie(0); cout.tie(0);
using namespace std ;
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace __gnu_pbds; 
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pll pair<ll, ll>
// ordered_set s ; s.order_of_key(val)  no. of elements strictly less than val
// s.find_by_order(i)  itertor to ith element (0 indexed)
//__builtin_popcount(n) -> returns number of set bits in n
 
 
ll get_ans(ll n, ll arr[] , ll bits, ll val)
{
    ll ans = inf ;
    map<ll ,ll> m ;
 
    ll curr_arr[n] ;
    for(int i = 0 ; i < n ; i++)
    {
        curr_arr[i] = ((arr[i]) >> (int)bits) ;
    }
 
    ll pre_xor = 0 ;
    m[0] = -1 ;
    for(int i = 0 ; i < n ; i++)
    {
        pre_xor ^= curr_arr[i] ;
        ll req_xor = (val ^ pre_xor) ;
 
        if(m.find(req_xor) == m.end())
        {
            m[pre_xor] = i ;
            continue ;
        }
 
        ll curr_ans = (i - m[req_xor]) ;
        ans = min(ans , curr_ans) ;
        m[pre_xor] = i ;
    }
    return ans ;
 
}
 
void solve()
{
    ll n, k ;
    cin >> n >> k ;
 
    ll arr[n] ;
    for(int i = 0 ; i < n ; i++)
        cin >> arr[i] ;
 
    ll curr_val = 0 ;
    ll ans = inf ;
 
    for(int i = 31 ; i >= 0 ; i--)
    {
        ll bit = ((1LL << i) & k) ;
        // cout << "bit = " << bit << endl ;
        curr_val *= 2 ;
 
        if(bit != 0)
        {
            curr_val++ ;
            continue ;
        }
 
        ans = min(ans , get_ans(n , arr , i , curr_val+1)) ;
        // cout << "i = " << i << " ans = " << ans << '\n' << endl ;
    }
    ans = min(ans , get_ans(n , arr , 0 , k)) ;
 
    if(ans == inf)
        ans = -1 ;
    cout << ans << endl ;
}
 
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    #ifndef ONLINE_JUDGE
    freopen("inputf.txt" , "r" , stdin) ;
    freopen("outputf.txt" , "w" , stdout) ;
    freopen("errorf.txt" , "w" , stderr) ;
    #endif
    ll t = 1;
    cin >> t ;
   
    while(t--)
    {
        solve() ;
    }
    // cerr << "Time : " << 1000 * ((double)clock()) / (double)CLOCKS_PER_SEC << "ms\n";
 
    return 0;
}