// sis puella oier
#include <bits/stdc++.h>
using namespace std;
#define int long long
typedef long long ll;
ll read(){
    ll xx = 0, f = 1; char ch = getchar();
    for (;!isdigit(ch); ch = getchar())
        f = (ch == '-' ? -1 : 1);
    for (; isdigit(ch); ch = getchar())
        xx = (xx << 3) + (xx << 1) + ch - '0';
    return xx * f;
}
int n, m, a[100100], b[100100], ans;
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 + n + 1), sort(b + 1, b + m + 1);
    b[0] = 0, b[m + 1] = a[n] + 1;
    ans = 0;
    for (int i = 0, l = 1, r = 1; i <= m; ++i){
        while(r <= n && a[r] < b[i + 1])++r;
        while(l <= n && a[l] <= b[i])++l;
        // cout<<i<<" "<<l<<" "<<r<<endl;
        ans = max(ans, r - l);
    }
    if (ans == 0){printf("Impossible\n");}
    else printf("%lld\n", ans);
}
signed main(){
    int _ = read();
    while(_--)solve();
    return 0;
}