#include <bits/stdc++.h>
using namespace std; 

int n, m; 
int a[100005], b[100005]; 

void solve(void) {
    cin >> n >> m; 
    for (int i = 1; i <= n; ++i) cin >> a[i]; 
    for (int i = 1; i <= m; ++i) cin >> b[i]; 
    sort(a + 1, a + n + 1); sort(b + 1, b + m + 1); b[m + 1] = 2e9; 
    int ans = 0; 
    for (int i = 0; i <= m; ++i) {
        int p1 = upper_bound(a + 1, a + n + 1, b[i]) - a; 
        int p2 = lower_bound(a + 1, a + n + 1, b[i + 1]) - a - 1; 
        ans = max(ans, p2 - p1 + 1); 
    }
    if (!ans) cout << "Impossible\n"; 
    else cout << ans << "\n"; 
}

int main(void) {
    ios::sync_with_stdio(0); cin.tie(0); 
    int T; cin >> T; 
    while (T--) solve();     
    return 0; 
}