#include<bits/stdc++.h>
#include<sstream>
#include<cassert>
#define fi first
#define se second
#define i128 __int128
using namespace std;
typedef long long ll;
typedef double db;
typedef pair<int,int> PII;
const double eps=1e-7;
const int N=5e5+7 ,M=5e5+7, INF=0x3f3f3f3f,mod=1e9+7,mod1=998244353;
const long long int llINF=0x3f3f3f3f3f3f3f3f;
inline ll read() {ll x=0,f=1;char c=getchar();while(c<'0'||c>'9') {if(c=='-') f=-1;c=getchar();}
while(c>='0'&&c<='9') {x=(ll)x*10+c-'0';c=getchar();} return x*f;}
inline void write(ll x) {if(x < 0) {putchar('-'); x = -x;}if(x >= 10) write(x / 10);putchar(x % 10 + '0');}
inline void write(ll x,char ch) {write(x);putchar(ch);}
void stin() {freopen("in_put.txt","r",stdin);freopen("my_out_put.txt","w",stdout);}
bool cmp0(int a,int b) {return a>b;}
template<typename T> T gcd(T a,T b) {return b==0?a:gcd(b,a%b);}
template<typename T> T lcm(T a,T b) {return a*b/gcd(a,b);}
void hack() {printf("\n----------------------------------\n");}

int T,hackT;
int n,m,k;
int a[N],b[N];

int get1(int x) {
	int l=0,r=n;
	while(l<r) {
		int mid=l+r+1>>1;
		if(a[mid]<x) l=mid;
		else r=mid-1;
	}
	return l;
}

int get2(int x) {
	int l=1,r=n+1;
	while(l<r) {
		int mid=l+r>>1;
		if(a[mid]>x) r=mid;
		else l=mid+1;
	}
	return l;
}

void solve() {
	n=read(),m=read();
	
	for(int i=1;i<=n;i++) a[i]=read();
	for(int i=1;i<=m;i++) b[i]=read();
	
	sort(a+1,a+1+n);
	sort(b+1,b+1+m);
	
	int res=0;
	res=max(res,get1(b[1])-get2(0)+1);
	res=max(res,get1(1000000001)-get2(b[m])+1);
	for(int i=2;i<=m;i++) {
		if(b[i]==b[i-1]) continue;
		res=max(res,get1(b[i])-get2(b[i-1])+1);
	}
	
	if(res==0) printf("Impossible\n");
	else printf("%d\n",res);
}   

int main() {
    // init();
    // stin();
	// ios::sync_with_stdio(false); 

    scanf("%d",&T);
    // T=1; 
    while(T--) hackT++,solve();
    
    return 0;       
}