#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const long long MAXN = 1e5 + 10;
const long long INF = 1e9 + 10;

inline long long read() {
	long long x = 0, f = 1;
	//register long long x = 0, f = 1;
	char ch = getchar();
	while (!isdigit(ch)) {
		if (ch == '-') f = -1;
		ch = getchar();
	}
	while (isdigit(ch)) {
		x = x * 10 + ch - '0';
		ch = getchar();
	}
	return x * f;
}

struct node {
	long long pos, c;
	bool operator < (const node &a) const {
		return pos < a.pos;
	}
} A[MAXN << 1];

long long a[MAXN], b[MAXN], n, m;
long long ans[MAXN];

int main() {
	long long t = read();
	for (long long u = 1; u <= t; u++) {
		n = read(); m = read();
		for (long long i = 1; i <= n; i++) a[i] = read();
		for (long long i = 1; i <= m; i++) b[i] = read();
		for (long long i = 0; i <= m + 1; i++) ans[i] = 0;
		sort(a + 1, a + 1 + n);
		sort(b + 1, b + 1 + m);
 		b[m + 1] = INF;
		long long j = 0;
		for (long long i = 1; i <= n; i++) {
			while (b[j + 1] <= a[i]) j++;
			if (b[j] != a[i]) ans[j]++;
		}
		long long Maxx = -1;
		for (long long i = 0; i <= m; i++) {
			Maxx = max(Maxx, ans[i]);
		}
		if (Maxx != 0)
			printf("%lld\n", Maxx);
		else 
			printf("Impossible\n");
	}
	return 0;
}