#include<bits/stdc++.h>
#define int long long
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const long long N=1e6+10,mod=998244353,INF=1e15;
ll n,m,k,a[N],b[N];
bool st[N];
void solve()
{
	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+1+n);
	sort(b+1,b+1+m);
	int ans=0;
	for(int i=1;i<=m-1;i++)
	{
		if(b[i]>=a[n])continue;
		int id=upper_bound(a+1,a+1+n,b[i])-a;
		int idx;
		if(b[i+1]>n)idx=n;
		else idx=lower_bound(a+1,a+1+n,b[i+1])-a-1;
		ans=max(ans,idx-id+1);
	}
	if(ans)cout<<ans<<endl;
	else cout<<"Impossible"<<endl;
}
signed main()
{
    cin.tie(0), cout.tie(0), ios::sync_with_stdio(false);
    int T;cin>>T;
    while(T--)solve();
    return 0;
}