#include<stdio.h>
#include<string.h>
#include<stdlib.h>

#define N 1000007

int M[N], S[N], Next[N];

void FindNext(int Slen)
{
    int i=0, j=-1;
    Next[0] = -1;

    while(i<Slen)
    {
        if(j==-1 || S[i]==S[j])
            Next[++i] = ++j;
        else
            j = Next[j];
    }
}



int KMP(int Mlen, int Slen)
{
    int i=0, j=0;

    FindNext(Slen);

    while(i<Mlen)
    {
        while(j==-1 || (M[i]==S[j] && i<Mlen && j<Slen))
            i++, j++;
        if(j==Slen)
            return i-Slen+1;

        j = Next[j];
    }
    return -1;
}

int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        int n, m, i;

        scanf("%d%d", &n, &m);

        for(i=0; i<n; i++)
            scanf("%d", &M[i]);
        for(i=0; i<m; i++)
            scanf("%d", &S[i]);

        printf("%d\n", KMP(n, m));
    }
    return 0;
}