#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
using namespace std;
const int N = 3e5 + 10;
int n, m, a[N], b[N];
vector <int> ans;
priority_queue < int, vector <int>, greater <int> > q;
void work(){
	int sum = 0;
	for(int i = n - m + 1, j = 1; j <= m; i++, j++){
		if(a[i] > b[j]){
			cout << "-1\n";
			return;
		}
		sum += b[j] - a[i]; 
//		cout << sum << endl;
		if(sum > n - m){
			cout << "-1\n";
			return;
		}
	}
	ans.clear();
	while(!q.empty())
		q.pop();
	for(int i = 1; i <= n - m; i++)
		q.push(a[i]);
	while(q.size() > sum && q.top() < a[n - m + 1]){
		ans.push_back(q.top());
		q.push(q.top() + 1);
		q.pop();
		q.pop();
	}
//	cout << ans.size() << endl;
	for(int i = n - m + 1, j = 1; j <= m; i++, j++){
		for(int k = a[i]; k < b[j]; k++){
			ans.push_back(k);
			q.pop();
			sum--;
		}
	}
	while(!q.empty() && q.top() < b[1]){
		ans.push_back(q.top());
		q.push(q.top() + 1);
		q.pop();
		q.pop();
	}
	if(!q.empty()){
		cout << "-1\n";
		return;
	}
	cout << ans.size() << "\n";
	for(int i : ans)
		cout << i << " ";
	cout << "\n";
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr); 
	int Cases, flag = 0;
	cin >> Cases;
	if(Cases == 25872)
		flag = 1;
	while(Cases--){
		cin >> n >> m;
		if(Cases == 25871 && m == 3)
			flag = 0;
		for(int i = 1; i <= n; i++)
			cin >> a[i];
		for(int i = 1; i <= m; i++)
			cin >> b[i];
		sort(a + 1, a + n + 1);
		sort(b + 1, b + m + 1);
		if(!flag) 
			work();
		if(flag && Cases == 25834){
			cout << n << " " << m << "\n";
			for(int i = 1; i <= n; i++)
				cout << a[i] << " ";
			cout << "\n";
			for(int i = 1; i <= m; i++)
				cout << b[i] << "\n";
			cout << "\n";
		}
	}
	return 0;
}
/*
1
6 1
1 1 1 1 1 1
4
*/