#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
#include <cmath>

using namespace std;
const int N = 1e5 + 5;
int n, m;

void solve(){
    
    cin >> n >> m;
    vector<int> a(n, 0), b(m, 0);
    for (int i = 0; i < n; i ++) cin >> a[i];
    for (int i = 0; i < m; i ++) cin >> b[i];
    sort(a.begin(), a.end());
    sort(b.begin(), b.end());

    int ans = 0;

    // auto pos1 = upper_bound(a.begin(), a.end(), 4);

    // cout << *pos1 << endl;


    for (int i = 0; i < m - 1; i ++){
        int l = b[i], r = b[i + 1];
        if (l == r) continue;
        // cout << l << ' ' << r << ' ';
        auto pos1 = upper_bound(a.begin(), a.end(), l);
       
        
        if (pos1 == a.end()){
            continue;
        }
        int p1 = pos1 - a.begin(), p2 = 0;

        auto pos2 = lower_bound(a.begin(), a.end(), r);


        if (pos2 == a.end()){
            p2 = n - 1;
            ans = max(ans, p2 - p1 + 1);
            continue;

        }

        if (*pos2 >= r){
            pos2 --;
        }
        p2 = pos2 - a.begin();

 
        ans = max(ans, p2 - p1 + 1);
        // cout << p1 << ' ' << p2 << ' ' << ans << endl;
    }

    // cout << "dwnoidnwon" << endl;

    if (ans){
        cout << ans << endl;
    }else{
        cout << "Impossible\n";
    }

    

}


int main(){
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;

    while (t --) solve();

}