void getNext(int *b,int m)
{
    Next[0]=-1;
    int i=0,j=-1;
    while(i<m&&j<m){
        if(j==-1||b[i]==b[j]) Next[++i]=++j;
        else j=Next[j];
    }
}

int kmp(int *a,int *b,int n,int m)
{
    getNext(b,m);
    int i=0,j=0;
    while(i<n&&j<m){
        if(j==-1||a[i]==b[j]) i++,j++;
        else j=Next[j];
    }
    if(j==m) return i-m;
    return -1;
}

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<vector>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<string>
#include<math.h>
#include<cctype>
#define ll long long
#define REP(i,a,b) for(int (i)=(a);(i)<=(b);(i)++)
#define REPP(i,a,b,t) for(int (i)=(a);(i)<=(b);(i)+=(t))
#define rep(i,a,b) for(int (i)=(a);(i)>=(b);(i)--)
#define repp(i,a,b,t) for(int (i)=(a);(i)>=(b);(i)-=(t))
#define PII pair<int,int>
#define fst first
#define snd second
#define MP make_pair
#define PB push_back
#define RI(x) scanf("%d",&(x))
#define RII(x,y) scanf("%d%d",&(x),&(y))
#define RIII(x,y,z) scanf("%d%d%d",&(x),&(y),&(z))
#define DRI(x) int (x);scanf("%d",&(x))
#define DRII(x,y) int (x),(y);scanf("%d%d",&(x),&(y))
#define DRIII(x,y,z) int (x),(y),(z);scanf("%d%d",&(x),&(y),&(z))
#define RS(x) scanf("%s",s)
#define RSS(x,y) scanf("%s%s",x,y)
#define DRS(x) char x[maxn];scanf("%s",x)
#define DRSS(x,y) char x[maxn],y[maxn];scanf("%s%s",x,y)
#define MS0(a) memset((a),0,sizeof((a)))
#define MS1(a) memset((a),-1,sizeof((a)))
#define MS(a,b) memset((a),(b),sizeof((a)))
#define ALL(v) v.begin(),v.end()
#define SZ(v) (v).size()

using namespace std;

const int maxn=1000100;
const int INF=(1<<29);
const double EPS=0.0000000001;
const double Pi=acos(-1.0);

int a[maxn],b[maxn];
int n,m;
int Next[maxn];

void getNext(int *b,int m)
{
    Next[0]=-1;
    int i=0,j=-1;
    while(i<m&&j<m){
        if(j==-1||b[i]==b[j]) Next[++i]=++j;
        else j=Next[j];
    }
}

int kmp(int *a,int *b,int n,int m)
{
    getNext(b,m);
    int i=0,j=0;
    while(i<n&&j<m){
        if(j==-1||a[i]==b[j]) i++,j++;
        else j=Next[j];
    }
    if(j==m) return i-m+1;
    return -1;
}

int main()
{
    DRI(T);
    while(T--){
        RII(n,m);
        REP(i,0,n-1) RI(a[i]);
        REP(i,0,m-1) RI(b[i]);
        cout<<kmp(a,b,n,m)<<endl;
    }
    return 0;
}