#include <bits/stdc++.h>
using namespace std;

int n, m, t, a[2005];
pair<int, int> b[2005];

int main() {
    cin >> t;
    while(t--) {
        cin >> n >> m;
        for(int i = 0; i < n; i++) {
            cin >> a[i];
            b[i] = {a[i], i + 1};
        }
        m -= (n * (n - 1)) / 2;
        if(m < 0) {
            cout << -1 << "\n";
            continue;
        }
        int cost = 0;
        vector<pair<int,int>> v;
        for(int i = 1; i <= n; i++) {
            for(int j = i + 1; j <= n; j++) {
                if(i == j) continue;
                cost += a[j] + a[i];
                v.push_back({i , j});
            }
        }
        sort(b, b + n);
        while(m--) {
            v.push_back({b[0].second , b[1].second});
            cost += b[0].first + b[1].first;
        }
        cout << cost << "\n";
        for(auto p : v)
            cout << p.first << " " << p.second << "\n";
    }
}