#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 = 2e5 + 5;
int ar[N], br[N];
int n, m;

int find(int x)
{
    int l = 0, r = n + 1;
    while (l + 1 < r)
    {
        int mid = (l + r) >> 1;
        if (ar[mid] >= x)
        {
            r = mid;
        }
        else
        {
            l = mid;
        }
    }
    return l;
}
void solve()
{
    cin >> n >> m;
    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 + 1, ar + 1 + n);
    sort(br + 1, br + 1 + m);

    int ans = -1;

    for (int i = 1; i <= m + 1; i++)
    {
        int l = upper_bound(ar, ar + n + 2, br[i - 1]) - ar;
        int r = find(br[i]);
        // cout << l << " " << r << endl;
        if (l >= n || l > r || r == 0)
            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;
}