#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 10;
int a[N], b[N];
int n, m;

int find(int x, int y) {
    int l = upper_bound(a+1, a + 1 +n, x) - a;
    int r = lower_bound(a+1, a + 1 +n, y) - a-1;
//    cout<<l<<' '<<r<<endl;
    return r - l + 1;
}

void solve(){
	
    cin >> n >> m;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    for (int i = 1; i <= m; i++)
        cin >> b[i];
    int ans = 0;
    b[m + 1] = 1e9 + 10;
    b[0] = -1e9 - 10;
    sort(a + 1, a + 1 + n);
    sort(b + 1, b + 1 + m);
    for (int i = 1; i <= m+1; i++) {
        int res = find(b[i - 1], b[i]);
        ans = max(ans, res);
    }
   	if(ans>0) cout<<ans<<endl;
   	else cout<<"Impossible"<<endl;
}

int main() {
    int T=1;
    cin >> T;
    while (T--) {
        solve();
    }
}