#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define pb push_back
#define ff first
#define ss second
#define all(x) x.begin(),x.end()
#define sz(s) (int)s.size()
#define pii pair<int,int>
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll T, n, a[N], t, tr, vis[N];
set <int> s;
vector <int> answer;
void solve(set<int> s) {
if(tr) return;
vector <int> v;
v.clear();
for(auto i : s) {
v.pb(i);
}
if(sz(v) == t) {
tr = 1;
cout << sz(answer) << '\n';
for(auto i : answer) {
cout << i << " ";
}
cout << '\n';
return;
}
for(int i = 1; i < sz(v) - 1; i++) {
if(vis[v[i + 1]] == 1 || vis[v[i-1]] == 1) continue;
s.erase(v[i - 1]);
s.erase(v[i + 1]);
answer.pb(v[i]);
solve(s);
answer.pop_back();
s.insert(v[i + 1]);
s.insert(v[i - 1]);
}
}
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> T;
while(T--) {
cin >> n >> t;
s.clear();
tr = 0;
answer.clear();
for(int i = 1; i <= n; i++) {
s.insert(i);
vis[i] = 0;
}
for(int i=1;i<=t;i++) {
cin >> a[i];
vis[a[i]] = 1;
}
solve(s);
if(!tr) cout << "-1\n";
}
}
