#include <bits/stdc++.h>
using namespace std;
#define int long long




void solve() {
	int n, m;
	cin >> n >> m;
	vector<int>a(n + 1);
	vector<int>b(m + 1);
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	for (int j = 1; j <= m; j++) {
		cin >> b[j];
	}
	sort(a.begin() + 1, a.end());
	sort(b.begin() + 1, b.end());
	int res = 0;
	for (int i = 1; i <= m; i++) {
		if (b[i] < a[i + n - m]) {
			cout << "-1" << endl;
			return;
		}
		if (b[i] > a[i + n - m]) {
			res += b[i] - a[i + n - m];
		}
	}
	priority_queue<int, vector<int>, greater<int>>q1, q2;
	for (int i = 1; i <= n - m; i++) {
		q1.push(a[i]);
	}
	for (int i = n - m + 1; i <= n; i++) {
		q2.push(a[i]);
	}
	int cnt = n - m - res;
	vector<int>ans;
	while (cnt) {
		cnt--;
		int x = q1.top();
		ans.push_back(x);
		q1.pop();
		if (x + 1 >= q2.top()) {
			q2.pop();
			q2.push(x + 1);
			cnt++;
		}
	}
	for (int i = 1; i <= m; i++) {
		int x = q2.top();
		q2.pop();
		if (x > b[i]) {
			cout << "-1" << endl;
			return;
		} else {
			for (; x < b[i];) {
				ans.push_back(x);
				x++;
			}
		}
	}
	cout << ans.size() << endl;
	for (int i = 0; i < ans.size(); i++) {
		cout << ans[i] << endl;
	}
	cout << endl;
	return;
}


signed main() {
	ios::sync_with_stdio(false);
	int tt = 1;
	cin >> tt;
	while (tt--) {
		solve();
	}
}