#include<bits/stdc++.h>
#define endl '\n'
#define int long long
#define pii pair<int, int>
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);  
#define rep(x,a,b) for(int x=a;x<=b;x++)
#define pre(x,a,b) for(int x=a;x>=b;x--)
using namespace std;
const int N = 1e6 + 10;
int n, m;
int a[N], b[N], c[N];
map<int, int>x, y;
void solve()
{   
    x.clear(), y.clear();
	cin >> n >> m;
    int idx = 0;
    rep(i, 1, n) cin >> a[i], c[++idx] = a[i];
    rep(i, 1, m) cin >> b[i], y[b[i]] = 1, c[++idx] = b[i];
    sort(c + 1, c + idx + 1);
    int ans = 0, len = 0;
    rep(i, 1, idx)
    {
        if(y[c[i]] != 1) len ++ ;
        else
        {
            ans = max(ans, len);
            len = 0;
            continue;
        }
    }
    ans = max(ans, len);
    if(!ans) cout << "Impossible" << endl;
    else
    cout << ans << endl;
}
signed main()
{
    IOS;
	int _;
	_ = 1;
	cin >> _;
	while(_--)
	{
	    solve();
	}
	return 0;
}