#include <bits/stdc++.h>
#define int long long
constexpr int N = 1e5 + 5;
constexpr int INF = 1e9 + 5;

int a[N], b[N];
void solve() {
    int n, m;
    std::cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        std::cin >> a[i];
    }
    for (int i = 1; i <= m; i++) {
        std::cin >> b[i];
    }
    std::sort(a + 1, a + n + 1);
    std::sort(b + 1, b + m + 1);
    a[n + 1] = INF;
    b[m + 1] = INF;
    int ans = 0;
    for (int i = 1; i <= m + 1; i++) {
        int left = b[i - 1], right = b[i];

        int it_left = std::upper_bound(a + 1, a + 1 + n, left) - a;
        int it_right = std::lower_bound(a + 1, a + 1 + n, right) - a;
        it_right--;
        ans = std::max(ans, it_right - it_left + 1);
    }
    if (ans == 0) std::cout << "Impossible\n";
    else std::cout << ans << '\n';
}

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

    int T;
    std::cin >> T;
    while (T--) {
        solve();
    }
}