/**
* In the name of Allah
* We are nothing and you're everything
* author: najmuddin
**/
#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("fast-math")
#pragma GCC optimize("trapv")
#pragma GCC optimize("inline")
using namespace std;
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
#define int ll
const char nl = '\n';
const int N = 1e8+5;
//const int inf = 1e18;
const int mod = 1e9+7;
void solve() {
int n, m;
cin >> n >> m;
if ((n-m)%2 ==1) {
cout << -1 << nl;
return;
}
map<int, int> mp, mp2;
vector<int> b;
for (int i = 0; i < m; ++i) {
int x; cin >> x;
b.push_back(x);
mp[x] = 1;
}
vector<int> a;
for (int i = 1; i <= n; ++i) {
if (mp[i] != 1)mp2[i] = 1;
}
vector<int> ans;
for (int i = 1; i <= n; ++i) {
if (mp2[i] == 1 && mp2[i+2] == 1 && (mp2[i+1] == 1 || mp[i+1] == 1)) {
mp2[i] = mp2[i+2] = 0;
ans.push_back(i+1);
}
if (mp2[i] == 1)a.push_back(i);
}
if (int(ans.size()) != (n - m) / 2) {
cout << -1 << nl;
return;
}
cout << sz(ans) << nl;
for (auto j: ans)cout << j << ' ';
cout << nl;
}
int32_t main() {
ios::sync_with_stdio(0);
cin.tie(0);
int t = 1;
cin >> t;
while (t--) {
solve();
}
return 0;
}
