int a[1100000],b[11000],n,m,next[11000],t;
void getNext()
{
next[1] = 0;
int i=1,j=0;
while(i<m)
{
if(j==0||b[i]==b[j]){
i++;
j++;
if(b[i]!=b[j]) next[i]=j;
else next[i]=next[j];
}
else j = next[j];
}
}
int kmp()
{
int i = 1,j = 1;
while(i<=n&&j<=m)
if(j==0||a[i]==b[j]){++i;++j;}
else j = next[j];
if(j==m+1)return i-m;
return -1;
}
int main()
{
scanf("%d",&t);
while(t--)
{
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)
scanf("%d",&a[i]);
for(int i=1;i<=m;i++)
scanf("%d",&b[i]);
getNext();
printf("%d\n",kmp());
}
}