#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int n,m;
void solve()
{
	
	scanf("%d %d",&n,&m);
	vector<int> a(n + 1),b(m + 1);
	map<ll,ll> q;
	for(int i = 1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		q[a[i]] ++;
	}
	for(int i = 1;i<=m;i++)
	{
		scanf("%d",&b[i]);
	}
	sort(a.begin() + 1,a.end());
	sort(b.begin() + 1,b.end());
	a.erase(unique(a.begin() + 1,a.end()),a.end());
	b.erase(unique(b.begin() + 1,b.end()),b.end());
	int i = 1;
	int j = 1;
	ll ans = 0;
	n = a.size() - 1;
	m = b.size() - 1;
//	for(int i = 1;i<=n;i++)
//	{
//		cout<<a[i]<<' ';
//	}
//	cout<<endl;
//	for(int i= 1;i<=m;i++)
//	{
//		cout<<b[i]<<' ';
//	}
//	cout<<endl;
	while(i <= n && j <= m)
	{
		ll cnt = 0;
		while(j <= m && b[j] <= a[i])
		{
			if(a[i] == b[j])
			{
				i ++;
				j ++;
			}
			else
			{
				j ++;
			}
		}
		if(j > m)
		{
			break;
		}
		while(i <= n && a[i] <= b[j])
		{
//			cout<<i<<' '<<a[i]<<endl;
			if(a[i] == b[j])
			{
				i ++;
				j ++;
				ans = max(ans,cnt);
				cnt = 0;
				continue;
			}
			else
			{
				cnt += q[a[i]];
				i ++;
				
			}
			
		}
//		cout<<i<<' '<<j<<' '<<cnt<<endl;
		ans = max(ans,cnt);
	}
	ll sum = 0;
	while(i <= n)
	{
		sum += q[a[i]];
		i ++;
	}
	ans = max(sum,ans);
	if(ans == 0)
	{
		puts("Impossible");
	}
	else
	{
		printf("%lld\n",ans);
	}
}

int main()
{
	int t = 1;
	scanf("%d",&t);
	while(t--)
	{
		solve();
	}
	return 0;
}