#include <bits/stdc++.h>

using i64 = long long;

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

    std::vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> a[i];
    }

    std::vector<int> b(m);
    for (int i = 0; i < m; ++i) {
        std::cin >> b[i];
    }
    b.push_back(0);
    b.push_back(1e9 + 1);

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

    int ans = 0;
    int p = 0, q = 0;
    for (int i = 0; i < int(b.size()) - 1; ++i) {
        while (p < n && a[p] <= b[i]) {
            ++p;
        }
        while (q < n && a[q] < b[i + 1]) {
            ++q;
        }
        ans = std::max(ans, q - p);
    }

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

int main() {
    std::cin.tie(nullptr)->sync_with_stdio(false);

    int t;
    std::cin >> t;

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

    return 0;
}