#include <bits/stdc++.h>
using namespace std;
const int N = 3e5 + 10;
int n,m;
int T;
int a[N];
int b[N];
bool cmp(int x,int y)
{
	return x > y;
}
multiset <int> st;
vector <int> v;
void init()
{
    while(!st.empty())st.erase(st.begin());
    while(!v.empty())v.pop_back();
}
int main()
{
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	cin >> T;
	while(T--)
	{
	    init();
		cin >> n >> m;
		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,cmp);
		sort(b + 1,b + m + 1,cmp);
		if(n < m){cout << -1 << endl;continue;}
		int flag = 1;
		int sum = 0;
		for(int i = 1;i <= m;i++)
        {
            if(a[i] > b[i]){flag = 0;break;}
            else{sum += b[i] - a[i];}
        }
        if(!flag){cout << -1 << endl;continue;}
        //st.clear();v.clear();
        for(int i = 1;i <= n;i++)
            st.insert(a[i]);
        int ed = a[m];
        int ans  =0;
        if(st.size() < m + sum)
        {
        	cout << -1 << endl;
        	continue;
		}
        while(st.size() > m + sum)
        {
            set <int>::iterator it = st.begin();
            if(*it >= ed){break;}
            else{
                st.erase(it);
                int val = *it;
                v.push_back(val);
                val ++;
                st.insert(val);
                st.erase(st.begin());
                ans++;
            }
        }
        for(int i = 1;i <= m;i++)
        {
            while(*st.rbegin() < b[i])
            {
                int val = *st.rbegin();
                set <int>::iterator it = st.find(val);
                v.push_back(val);
                val++;
                ans++;
                st.erase(it);
                st.insert(val);
                st.erase(st.begin());
            }
            if(*st.rbegin() == b[i])
            {
                int tt = *st.rbegin();
                set <int>::iterator it = st.find(tt);
                st.erase(it);
            }
            else{flag = 0;break;}
        }
        if(!flag){cout << -1 << endl;continue;}
        while(!st.empty())
        {
            set <int>::iterator it = st.begin();
            int val = *it;
            if(val == b[m]){flag = 0;break;}
            ans++;
            v.push_back(val);
            val++;
            st.erase(it);
            st.insert(val);
            st.erase(st.begin());
        }
        if(!flag){cout << -1<< endl;continue;}
        cout <<ans << endl;
        int len = v.size();
        for(int i = 0;i < len;i++)
            cout << v[i] << " ";
        if(ans)cout << endl;
	}
	return 0;
}