#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+5;
int T,n,k,a[maxn],b[maxn];
const int maxm=6e6+5;
int ch[maxm][2],tot,sum[maxm];
void clear() {
    for(int i=0;i<=tot;++i) ch[i][0]=ch[i][1]=sum[i]=0;
    tot=0;
}
void insert(int now,int p,int x) {
	sum[now]++;
	if(p==-1) return;
	int w=(x>>p)&1;
	if(!ch[now][w]) ch[now][w]=++tot;
	insert(ch[now][w],p-1,x);
}
void del(int now,int p,int x) {
	sum[now]--;
	if(p==-1) return;
	int w=(x>>p)&1;
	del(ch[now][w],p-1,x);
}
int query(int now,int p,int x) {
	if(p==-1) return x;
	int w=(x>>p)&1;
	if(ch[now][w]&&sum[ch[now][w]]) return query(ch[now][w],p-1,x^(w<<p));
	else return query(ch[now][!w],p-1,x|(1<<p));
}
int main() {
	//ios::sync_with_stdio(0);
	//cin.tie(0);
	cin>>T;
	while(T--) {
		cin>>n>>k;
		int tmp=0;
		for(int i=1;i<=n;++i) {
			cin>>a[i];
			tmp^=a[i];
			if(a[i]==0) b[i]=-1;
			else b[i]=(a[i]^(a[i]-1)),insert(0,30,b[i]);
		}
		int ans=0;
		for(int i=1;i<=n;++i) {
			int now=tmp^a[i]^(a[i]+1);
			if(a[i]) del(0,30,b[i]);
			insert(0,30,a[i]^(a[i]+1));
			ans=max(ans,query(0,30,now));
			del(0,30,a[i]^(a[i]+1));
			if(a[i]) insert(0,30,b[i]);
		}
		cout<<ans<<'\n';
		clear();
	}
	return 0;
}