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

using namespace std;

const int N = 1e5 + 10;
int n, m, a[N], b[N];

void solve()
{
    cin >> n >> m;
    set<int>s;
    for (int i = 1; i <= n; i++)cin >> a[i];
    for (int i = 1; i <= m; i++)cin >> b[i], s.insert(b[i]);
    sort(a + 1, a + n + 1);
    bool ok = 0;
    int ans = 0;
    for (int i = 1; i <= n; i++)
    {
        if (!s.count(a[i])) {
            ok = 1, ans = 1;
            break;
        }
    }
    if (!ok)cout << "Impossible\n";
    else {
        int pre = 0;
        a[n + 1] = 1e9 + 7;
        for (int i = 1; i <= n; i++) {
            auto it = s.lower_bound(a[i]);
            if (s.count(a[i])) {
                ans = max(ans, pre);
                pre = 0;
                continue;
            }
            if (it != s.end() && (*it) >= a[i] && (*it) <= a[i + 1]) {
                ans = max(ans, pre + 1);
                pre = 0;
                continue;
            }
            else {
                pre++;
            }
        }
        ans = max(ans, pre);
        cout << ans << '\n';
    }
}

int main()
{
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1; cin >> t;
    while (t--)solve();
    return 0;
}