#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=5e5+5,M=3e5+5,K=(1<<15)+5,mod=998244353,Mod=mod-1;const db eps=1e-9;const int INF=1e9+7;mt19937 rnd(time(0));
int n,m,A[N],B[N];
void Solve(){
	int i,j;scanf("%d%d",&n,&m);
	for(i=1;i<=n;i++) scanf("%d",&A[i]);
	for(i=1;i<=m;i++) scanf("%d",&B[i]);
	sort(A+1,A+n+1);sort(B+1,B+m+1);
	int ans=-1;
	B[0]=0;B[m+1]=1e9+7;
	for(i=0;i<=m;i++){
		int p=LB(A+1,A+n+1,B[i+1])-A-1;
		int q=UB(A+1,A+n+1,B[i])-A;
		if(q<=p) ans=max(p-q+1,ans);
	}
	if(ans==-1) puts("Impossible");
	else printf("%d\n",ans);
}
int main(){
	int t;
	scanf("%d",&t);
	// t=1;
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}