#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define mp make_pair
typedef long long ll;
const int N=2e5+5;
const int mod=1e9+7;
const int inf=0x3f3f3f3f;
const ll INF=1e18+3;
#define DEBUG 
#ifdef DEBUG
#define debug(x...) cerr<<"["#x"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(x)
#else
#define debug(...) {}
#endif
//debug(n,m);debug("a,b");
//double max:0x7f,0x43 min:0xfe 0x c2  int:0x3f 
//运算符 priority  后缀 前缀 */+- 位移 比较 &^| && || 赋值

void solve()
{
    int n,m;
    cin>>n>>m;
    vector<int> a(n),b(m),ans,res;
    for(int i=0;i<n;i++) cin>>a[i];
    for(int i=0;i<m;i++) cin>>b[i];
    sort(a.begin(),a.end());
    sort(b.begin(),b.end());
    int k=0,p1=n-1,p2=m-1;
    while(k<n-m && p2>=0){
        if(a[p1]>b[p2] || k>p1) {
            cout<<-1<<'\n';
            return;
        }
        for(int i=a[p1];i<b[p2];i++) ans.push_back(i);
        k+=b[p2]-a[p1];
        a[p1]=b[p2];
        p2--,p1--;
    }
    //debug(p1,p2);
    priority_queue<int,vector<int>,greater<int>> q;
    //debug(k);
    p1=0;
    while(k<n-m){
        q.push(a[p1]),k++,p1++;
    }
    //debug(q.size());
    while(!q.empty()){
        int x=q.top();
        q.pop();
        res.push_back(x);
        //debug(x);
        if(q.empty()){
            if(x==b[0]){
                cout<<"-1\n";
                return;
            }
        }
        q.push(x+1);
        q.pop();
    }
    cout<<ans.size()+res.size()<<'\n';
    for(auto i:res) cout<<i<<" ";
    for(auto i:ans) cout<<i<<" ";
    cout<<'\n';
    return;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    #if 1 
        int T; cin>>T; while(T--) solve();
    #else 
        solve();
    #endif 
    return 0; 
}