#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>

#define ll long long
#define pb push_back
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define ios ios_base::sync_with_stdio(false);cin.tie(NULL)
#define ld long double
#define li __int128

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<int D, typename T>struct vec : public vector<vec<D - 1, T>> {template<typename... Args>vec(int n = 0, Args... args) : vector<vec<D - 1, T>>(n, vec<D - 1, T>(args...)) {}};
template<typename T>struct vec<1, T> : public vector<T> {vec(int n = 0, T val = T()) : vector<T>(n, val) {}};
template<class T1,class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
int ri(){int x;scanf("%i",&x);return x;}
void rd(int&x){scanf("%i",&x);}
void rd(long long&x){scanf("%lld",&x);}
void rd(double&x){scanf("%lf",&x);}
void rd(long double&x){scanf("%Lf",&x);}
void rd(string&x){cin>>x;}
void rd(char*x){scanf("%s",x);}
template<typename T1,typename T2>void rd(pair<T1,T2>&x){rd(x.first);rd(x.second);}
template<typename T>void rd(vector<T>&x){for(T&p:x)rd(p);}
template<typename C,typename...T>void rd(C&a,T&...args){rd(a);rd(args...);}
//istream& operator>>(istream& is,__int128& a){string s;is>>s;a=0;int i=0;bool neg=false;if(s[0]=='-')neg=true,i++;for(;i<s.size();i++)a=a*10+s[i]-'0';if(neg)a*=-1;return is;}
//ostream& operator<<(ostream& os,__int128 a){bool neg=false;if(a<0)neg=true,a*=-1;ll high=(a/(__int128)1e18);ll low=(a-(__int128)1e18*high);string res;if(neg)res+='-';if(high>0){res+=to_string(high);string temp=to_string(low);res+=string(18-temp.size(),'0');res+=temp;}else res+=to_string(low);os<<res;return os;}

void test(){
	int n=ri(),m=ri();
	vector<int> a;
	vector<int> b;
	for(int i=0;i<n;i++){
		int r=ri();
		a.pb(r);
	}
	for(int i=0;i<m;i++){
		int r=ri();
		b.pb(r);
	}
	sort(rall(a));
	sort(rall(b));
	int treba=sz(a)-sz(b);
	vector<int> ans;
	for(int i=0;i<sz(b);i++){
		int o=b[i]-a[i];
		if(o<0||o>treba){
			printf("-1\n");
			return;
		}
		for(int j=a[i];j<b[i];j++){
			ans.pb(j);
		}
		treba-=o;
	}
	sort(all(ans));
	int mxAns=sz(ans);
	int ind=0;
	while(treba){
		int tr=a.back();
		if(tr==b.back())break;
		int cnt=0;
		while(sz(a)>sz(b)&&a.back()==tr){
			a.pop_back();
			cnt++;
		}
		int vecUzeo=0;
		while(ind<mxAns&&ans[ind]==tr){
			cnt++;
			vecUzeo++;
			ind++;
			a.pop_back();
		}
		int mogu=cnt-cnt/2;
		mogu-=vecUzeo;
		if(mogu>=treba){
			for(int i=0;i<treba;i++)ans.pb(tr);
			treba=0;
			break;
		}
		assert(mogu>=0);
		mogu+=vecUzeo;
		for(int i=0;i<mogu;i++)ans.pb(tr);
		for(int i=0;i<mogu;i++)a.pb(tr+1);
		if(cnt&1){
			if(mogu==vecUzeo){
				break;
			}
			a.pop_back();
		}
		treba-=mogu-vecUzeo;
	}
	if(treba){
		printf("-1\n");
		return;
	}
	sort(all(ans));
	printf("%i\n",sz(ans));
	for(auto p:ans){
		printf("%i ",p);
	}
	printf("\n");
}
int main()
{
	int t=ri();
	while(t--){
		test();
	}
	return 0;
}