// Code by Heratino & Nelofus
// Narcissus & どうか安寧な記憶を

#include <bits/stdc++.h>
using i64 = long long;

//{{{星光闪耀
template<typename Ta, typename Tb>
inline void chkmax(Ta &a, const Tb &b) {if (a < b)	a = b;}
template<typename Ta, typename Tb>
inline void chkmin(Ta &a, const Tb &b) {if (a > b)	a = b;}
char buf[1 << 20], *P1, *P2;
inline char gc() {
	if (P1 == P2)
		P2 = (P1 = buf) + fread(buf, 1, 1 << 20, stdin);
	return P1 == P2 ? EOF : *P1++;
}
template<typename T>
inline void read(T &ans) {
	ans = 0;
	T w = 1;
	char c = gc();
	while (!isdigit(c)) {
		if (c == '-')	w = -1;
		c = gc();
	}
	while (isdigit(c)) {
		ans = (ans << 3) + (ans << 1) + (c ^ 48);
		c = gc();
	}
	ans *= w;
}
template<typename T, typename ...Ts>
void read(T &a, Ts&... other) {
	read(a);
	read(other...);
}
//}}}

void solve() {
	int n, m;
	read(n, m);
	std::vector<int> a(n);
	std::vector<int> b(m);
	for (int &x : a)	read(x);
	for (int &x : b)	read(x);
	std::sort(a.begin(), a.end());
	std::sort(b.begin(), b.end());

	int ans = 0;
	for (int i = 0; i < m - 1; i++) {
		int l = std::upper_bound(a.begin(), a.end(), b[i]) - a.begin();
		int r = (int)(std::lower_bound(a.begin(), a.end(), b[i + 1]) - a.begin()) - 1;
		chkmax(ans, r - l + 1);
	}
	int front = (int)(std::lower_bound(a.begin(), a.end(), b[0]) - a.begin()) - 1;
	chkmax(ans, front - 0 + 1);
	int back = std::upper_bound(a.begin(), a.end(), b.back()) - a.begin();
	chkmax(ans, n - 1 - back + 1);
	if (ans)
		std::cout << ans << '\n';
	else
		std::cout << "Impossible" << '\n';
}

int main() {
#ifdef HeratinoNelofus
	freopen("input.txt", "r", stdin);
#endif

	int T;
	read(T);
	while (T--) {
		solve();
	}
	return 0;
}