//
// Created by travel on 2024/10/11.
//
#include<bits/stdc++.h>
using namespace std;
#define int long long
typedef pair<int,int> PII;
#define endl "\n"
#define ft first
#define sd second
#define pb push_back
const int mod = 1e9 + 7;
int n,m;
const int N = 1e5 + 10;
int a[N],b[N];
void solve(){
    cin>>n>>m;
    vector<PII> v;
    map<int,int> mp,st;
    for(int i = 1;i <= n;i++){
        cin>>a[i];
        mp[a[i]]++;
    }
    for(int i = 1;i <= m;i++){
        cin>>b[i];
        if(mp.count(b[i])){
            st[b[i]] = 1;
        }
    }
    for(int i = 1;i <= n;i++){
        if(!st[a[i]]) v.push_back({a[i],1});
    }
    for(int i = 1;i <= m;i++)
        if(!st[b[i]]) v.push_back({b[i],0});
    sort(v.begin(),v.end());
    int maxv = 0,last = -1,cnt = 1;
    for(int i = 0;i < v.size();i++){
        if(i == 0) last = v[i].second,cnt = 1;
        else if(i == v.size() - 1){
            if(last == 1 && v[i].second == 1)
            {
                maxv = max(maxv,cnt + 1);
            }
            else if(last == 1 && v[i].second == 0)
                maxv = max(maxv,cnt);
            else if (last == 0 && v[i].second == 1)
                maxv = max(maxv,1ll);
        }
        else{
            if(last != v[i].second)
            {
                if(last == 1) maxv = max(maxv,cnt);
                last = v[i].second;
                cnt = 1;
            }
            else cnt++;
        }
    }
    if(maxv == 0) cout<<"Impossible"<<endl;
    else cout<<maxv<<endl;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int T ; cin>>T;
    while(T--)
        solve();
    return 0;
}