#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stack>
#include<set>
#include<queue>
#include<vector>
#include<iostream>
#include<algorithm>
#define MAXN 1010100
#define LL long long
#define ll __int64
#define INF 0x7fffffff
#define cs(s) freopen(s,"r",stdin)
#define mem(x) memset(x,0,sizeof(x))
#define PI acos(-1)
#define eps 1e-10
using namespace std;
int gcd(int a,int b){return b?gcd(b,a%b):a;}
int lcm(int a,int b){return a/gcd(a,b)*b;}
LL powmod(LL a,LL b,LL MOD){LL ans=1;while(b){if(b%2)ans=ans*a%MOD;a=a*a%MOD;b/=2;}return ans;}
//head
int t,m,n;
int pattern[1101001],text[1001001];
vector <int> find_substring(int pattern[],int text[]){
	vector<int> nex (n+1,0);
	for(int i=1;i<n;i++){
		int j=i;
		while(j>0) {
		    j=nex[j];
		    if(pattern[j]==pattern[i]){nex[i+1]=j+1;break;}
		}
	}
	vector<int>pos;
	for(int i=0,j=0;i<m;i++){
		if(j<n&&text[i]==pattern[j])j++;
		else{
			while(j>0){
				j=nex[j];
				if(text[i]==pattern[j]){
					j++;
					break;
				}
			}
		}
		if(j==n)pos.push_back(i-n+1);
	}
	return pos;
}
int main(){
	ios::sync_with_stdio(false);
	for(cin>>t;t;t--){
		cin>>m>>n;
		for(int i=0;i<m;i++)cin>>text[i];
		for(int i=0;i<n;i++)cin>>pattern[i];
		vector<int>ans=find_substring(pattern,text);
		if(!ans.size())cout<<-1<<'\n';
		else cout<<ans[0]+1<<'\n';
	}
	return 0;
}