#include <bits/stdc++.h>
using namespace std;
#define ll long long
// #define int ll
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define REP(i, n) FOR(i, 0, n)
#define REP1(i, n) FOR(i, 1, n+1)
#define RREP(i, n) for (int i = (n)-1; i >= 0; i--)
#define pii pair<int, int>
#define pip pair<int, pii>
#define f first
#define s second
#define pb push_back
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) (int)((x).size())
#define endl '\n'
#ifdef TOAD
#define IOS() ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#else
#define IOS() ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
#endif // TOAD
const ll maxn = 1e3+5;
const int iinf = 1e9+5;
signed main(){
IOS();
int t; cin>>t;
while(t--){
int n, q; cin>>n>>q;
vector<bool> toad(n+1);
vector<int> rem(q), del;
REP(i, q){
cin>>rem[i];
toad[rem[i]] = 1;
}
int lick = -1;
REP1(i, n){
if (i > 0 && i < n && !toad[i-1] && toad[i] && !toad[i+1]){
lick = i;
}
}
REP1(i, n){
if (!toad[i]) del.pb(i);
}
vector<vector<int>> nip;
int pre = -3;
for (auto x:del){
if (x-pre > 2){
vector<int> poo; poo.pb(x);
nip.pb(poo);
}
else nip.back().pb(x);
pre = x;
}
bool gg = false;
vector<int> ians;
for (auto vv:nip){
if (SZ(vv)&1) gg = 1;
bool ex = 0;
REP(i, SZ(vv)-1) if (vv[i+1] > vv[i]+1) ex = 1;
if (!ex) gg = 1;
int cnt = 0;
vector<int> oo;
REP(i, SZ(vv)){
cnt++;
if (i == SZ(vv)-1 || vv[i+1] != vv[i]+1){
oo.pb(cnt);
cnt = 0;
}
}
if (gg) break;
/*bool fang = 0;
REP(i, SZ(oo)-1){
if (oo[i] < 0){
gg = 1;
break;
}
if (oo[i] == 0) {
fang = 0;
continue;
}
if (oo[i]&1){
oo[i+1]--;
fang = 1;
}
else {
oo[i+1] -= 2;
if (oo[i+1] == -1){
if (fang){
oo[i+1] += 2;
fang = 0;
}
else{
gg = 1;
break;
}
}
else fang = 1;
}
}
if (oo.back() < 0 || (oo.back() > 0 && !fang)){
gg = 1;
break;
}*/
if (oo[0] <= oo[1]){
int penis = (oo[1] - oo[0])/2;
for (int i = penis; i >= 1; i--){
ians.pb(lick + 2*i);
}
REP(i, oo[0]) ians.pb(lick);
}
else{
int penis = (oo[0] - oo[1])/2;
for (int i = penis; i >= 1; i--){
ians.pb(lick - 2*i);
}
REP(i, oo[1]) ians.pb(lick);
}
}
if (gg){
cout<<-1<<endl;
}
else{
cout<<SZ(ians)<<endl;
for (auto x:ians) cout<<x<<' ';
cout<<endl;
}
//cout<<(gg?-1:0)<<endl;
}
}
/*
2 3
2 4 3
5 7 5
*/
