/*
    /\_/\
   (= ._.)
   / >  \>
*/
#include <iostream>
#include <cstring>
#include <string>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <cstdio>
#include <cmath>
#include <cassert>
#define int long long
#define double long double
using namespace std;
const int N = 1e5 + 10, M = 1e6 + 10, MOD = 1e9 + 7;
int a[N], b[N];
void solve() {
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= n; i++) cin >> a[i];
	for (int i = 1; i <= m; i++) cin >> b[i];
	map<pair<int, int>, int> mp;
	for (int i = 1; i <= m; i++) {
		mp[ {b[i], 1}]++;
	}
	for (int i = 1; i <= n; i++) {
		if (mp[ {a[i], 1}] != 0) continue;
		mp[ {a[i], 0}]++;
	}
	int ans = 0, res = 0;
	for (auto i : mp) {
		if (i.second == 0) continue;
		//cout << i.first.first << ' ' << i.first.second << ' ' << i.second << '\n';
		if (i.first.second == 0) {
			res += i.second;
		} else {
			ans = max(ans, res);
			res = 0;
		}
	}
	if (ans == 0) cout << "Impossible\n";
	else cout << ans << '\n';
}
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int TT = 1;
	cin >> TT;
	while (TT--) {
		solve();
	}
	return 0;
}
/*
    /\_/\
   (= ._.)
   / >  \>

   3

   2 2
   2 3
   1 4

   6 5
   1 2 3 5 7 7
   1 3 3 4 10

   1 1
   7
   7

*/