#include<bits/stdc++.h>
#define LL long long
#define eb emplace_back
#define pii pair<int,int>
#define fr first
#define sc second
#define mp make_pair
using namespace std;
const int infi=1e9;

int n,m;
void solve()
{
	cin>>n>>m;vector<int> a(n+1,0),b(m+1,0);
	for(int i=1;i<=n;++i) cin>>a[i];
	for(int i=1;i<=m;++i) cin>>b[i];
	sort(a.begin()+1,a.end(),greater<int>());
	sort(b.begin()+1,b.end(),greater<int>());
	LL sum=0;multiset<int> st1,st2;
	for(int i=1;i<=m;++i)
	{
		if(a[i]>b[i]) return cout<<"-1\n",void();
		st1.insert(a[i]);sum+=b[i]-a[i];
	}
	if(sum>n-m) return cout<<"-1\n",void();
	for(int i=1;i<=n;++i) st2.insert(a[i]);
	vector<int> ans;
	while(sum<n-m)
	{
		int x=*st2.begin();st2.erase(st2.find(x));
		ans.eb(x);
		st2.insert(++x);
		if(x>*st1.begin())
		{
			sum--;
			if(sum<0) return cout<<"-1\n",void();
			st1.erase(st1.begin());
			st1.insert(x);
		}
		st2.erase(st2.begin());
		--n;
	}
	for(int i=m;i;--i) a[i]=*st1.begin(),st1.erase(st1.begin());
	for(int i=1;i<=m;++i)
		for(int j=a[i];j<b[i];++j)
			ans.eb(j);
	cout<<ans.size()<<'\n';
	for(auto x:ans) cout<<x<<' ';
	cout<<'\n';
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	int TT=1;
	cin>>TT;
	for(;TT;--TT) solve();
}