#include<iostream>
#include<vector>
#include<algorithm>
#include<utility>
#include<cmath>
using namespace std;
typedef long long ll;
const ll inf = 1e18;
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
int t;
cin >> t;
while(t--){
int n, k;
cin >> n >> k;
vector<pair<int, pair<int, int>>> rngs;
vector<int> vec(n + 1);
for(int i = 0; i < k; i++){
int tmp;
cin >> tmp;
vec[tmp] = 1;
}
int lst = 1;
for(int i = 2; i <= n; i++){
if(vec[i - 1] != vec[i]){
rngs.emplace_back(vec[i - 1], make_pair(lst, i - 1));
lst = i;
}
}
rngs.emplace_back(vec[n], make_pair(lst, n));
if(rngs.back().first == 1) rngs.pop_back();
if(!rngs.empty() && rngs[0].first == 1){
rngs.erase(rngs.begin());
}
int sum = 0;
int cnt = 0;
bool flag = 0;
vector<pair<int, int>> vals;
for(auto &[val, info]: rngs){
auto &[l, r] = info;
if(val == 1){
if(l < r){
if(sum % 2 == 1 || cnt == 1){
flag = 1;
break;
}
sum = 0;
cnt = 0;
}
}
else sum += r - l + 1, cnt++, vals.emplace_back(l, r);
}
if(sum % 2 == 1 || cnt == 1){
flag = 1;
}
if(flag){
cout << "-1\n";
continue;
}
cout << (n - k) / 2 << "\n";
vector<int> ans;
int a = vals[0].second - vals[0].first + 1, b = vals[1].second - vals[1].first + 1, mid = vals[0].second + 1;
if(a == b){
for(int i = 0; i < a; i++) ans.push_back(mid);
}
else if(a > b){
for(int i = 0; i < b; i++) ans.push_back(mid);
a -= b;
int mid2 = mid - a / 2 - 1;
for(int i = 0; i < a / 2; i++) ans.push_back(mid2);
}
else{
for(int i = 0; i < a; i++) ans.push_back(mid);
b -= a;
int mid2 = mid + b / 2 + 1;
for(int i = 0; i < b / 2; i++) ans.push_back(mid2);
}
reverse(ans.begin(), ans.end());
for(auto &x: ans) cout << x << " ";
cout << "\n";
}
}
// g++ -std=c++17 -Wall -Wextra -Wshadow -fsanitize=undefined -fsanitize=address -o run pB.cpp -g
