#include <cstdio>
#include <algorithm>
#define N 100005
#define LGA 35
#define ctz __builtin_ctz
using namespace std;

const int lga = 29;

int T, n, s, ans, a[N], cnt[LGA];

int main ()
{
	scanf ("%d", &T);
	while (T --)
	{
		scanf ("%d%*d", &n), s = 0;
		for (int i = 0; i <= lga; i ++) cnt[i] = 0;
		for (int i = 1; i <= n; i ++)
		{
			scanf ("%d", &a[i]), s ^= a[i];
			if (a[i]) cnt[ctz (a[i])] ++;
		}
		for (int i = 1, res; res = s, i <= n; i ++)
		{
			if (a[i]) cnt[ctz (a[i])] --;
			for (int j = 0; j <= lga; j ++) if (cnt[j])
			{
				int now = s ^ a[i] ^ a[i] + 1;
				now ^= 1 << j ^ (1 << j) - 1;
				res = min (res, now);
			}
			ans = max (ans, res);
			if (a[i]) cnt[ctz (a[i])] ++;
		}
		printf ("%d\n", ans);
	}
	return 0;
}

/*
1
2 1
1 3
*/