#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<queue>
#include<map>
#include<vector>
#include<stack>
#define int long long
#define endl '\n'
using namespace std;
typedef pair<int,int> PII;
const int N=200200;
int n,m;
int a[N],b[N];
int find(int x){
	int l=0,r=n+1;
	while(l<r){
		int mid=(l+r)/2;
		if(a[mid]>x){
			r=mid;
		}
		else l=mid+1;
	}
	return l;
}
int find2(int x){
	int l=0,r=n+1;
	while(l<r){
		int mid=(l+r+1)/2;
		if(a[mid]<x){
			l=mid;
		}
		else r=mid-1;
	}
	return l;
}
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+n+1);
	sort(b+1,b+1+m);
	b[0]=0;
	b[m+1]=1e9+10;
	a[n+1]=1e9+10;
	int ans=0;
	for(int i=0;i<=m;i++){
		int l=find(b[i]);
		int r=find2(b[i+1]);
		//cout<<" "<<l<<" "<<r<<endl;
		if(l==n+1||r==0||r-l<0) continue;
		ans=max(r-l+1,ans);
	}
	if(ans==0){
		cout<<"Impossible"<<endl;
		return;
	}
	cout<<ans<<endl;
}
signed main(){
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int T=1;
	cin>>T;
	while(T--){
		solve();
	}
	return 0;
}