/* name: K
 * author: 5ab
 * created at: 2024-06-24
 */
#include <bits/stdc++.h>
using namespace std;

#define all(x) (x).begin(), (x).end()
#define ssz(x) (int((x).size()))

auto chmax = [](auto& x, auto y) { if (x < y) x = y; };
auto chmin = [](auto& x, auto y) { if (y < x) x = y; };

using ll = long long;
const int N = 1e5, lgA = 30;

int a[N], c[lgA];

signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int cas, n, k;
	
	auto lb = [&](int x) { return __lg(x & -x); };
	auto gm = [&](int x) { return (1 << (x + 1)) - 1; };
	auto ad = [&](int x, int v)
	{
		if (x != 0)
			c[lb(x)] += v;
	};
	
	cin >> cas;
	while (cas--)
	{
		cin >> n >> k;
		fill(c, c + lgA, 0);
		
		int sm = 0;
		for (int i = 0; i < n; i++)
		{
			cin >> a[i];
			ad(a[i], 1);
			sm ^= a[i];
		}
		int ans = 0;
		for (int i = 0; i < n; i++)
		{
			int cv = sm, lbc = lb(a[i] + 1);
			ad(a[i], -1), ad(a[i] + 1, 1);
			for (int j = 0; j < lgA; j++) if (c[j])
			{
				chmin(cv, sm ^ gm(j) ^ gm(lbc));
				// cerr << j << " " << lbc << " " << cv << endl;
			}
			chmax(ans, cv);
			ad(a[i], 1), ad(a[i] + 1, -1);
		}
		cout << ans << endl;
	}
	
	return 0;
}
// started coding at: 06-24 10:09:52