#include <bits/stdc++.h>
using namespace std;
#define IOS ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define int long long
#define lb(x) (x & (-x))
#define endl '\n'
#define INF LONG_LONG_MAX
#define eps 1e-7
typedef pair<int, int> PII;
const int N = 2e2 + 5;

void solve()
{
    int n, m;
    cin >> n >> m;
    vector<int> ar(n + 2), br(m + 2);
    for (int i = 1; i <= n; i++)
        cin >> ar[i];
    for (int i = 1; i <= m; i++)
        cin >> br[i];
    ar[0] = br[0] = 0;
    ar[n + 1] = br[m + 1] = INF;
    sort(ar.begin(), ar.end());
    sort(br.begin(), br.end());
    int ans = -1;

    for (int i = 2; i <= m; i++)
    {
        int l = upper_bound(ar.begin(), ar.end(), br[i - 1]) - ar.begin();
        int r = lower_bound(ar.begin(), ar.end(), br[i]) - ar.begin();
        r--;
        if (l >= n || l > r)
            continue;

        ans = max(ans, r - l + 1);
    }
    if (ans == -1)
        cout << "Impossible" << endl;
    else
        cout << ans << endl;
}
signed main()
{
    // IOS;
    int tcase;
    cin >> tcase;
    while (tcase--)
        solve();
    return 0;
}