#include <bits/stdc++.h>
#define int long long

using namespace std;

constexpr int inf = 1E18;

void solve () {
    int n, m;
    cin >> n >> m;

    vector <int> a (n), b (m);
    for (int i = 0; i < n; i ++) {
        cin >> a[i];
    }
    for (int i = 0; i < m; i ++) {
        cin >> b[i];
    }
    b.push_back (-inf);
    b.push_back (inf);

    sort (a.begin (), a.end ());
    sort (b.begin (), b.end ());

    int ans = 0;
    for (int i = 0; i < m + 1; i ++) {
        int l = upper_bound (a.begin (), a.end (), b[i]) - a.begin ();
        int r = lower_bound (a.begin (), a.end (), b[i + 1]) - a.begin ();
        if (r != 0) {
            r --;
            ans = max (ans, r - l + 1);
        }
    }

    if (ans == 0) {
        cout << "Impossible\n";
    } else {
        cout << ans << '\n';
    }
}

signed main () {
    ios::sync_with_stdio (false);
    cin.tie (nullptr);

    int T = 1;
    cin >> T;

    while (T --) {
        solve ();
    }

    return 0;
}