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

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int t;
    cin >> t;
    while (t--)
    {
        int n;
        cin >> n;

        int tot = 0;
        map<int, int> idx, idy;
        vector<set<pair<int, int>>> adj(n * 4 + 1);
        for (int i = 1, x, y; i <= n * 2; i++)
        {
            cin >> x >> y;
            if (!idx.count(x))
                idx[x] = ++tot;
            if (!idy.count(y))
                idy[y] = ++tot;
            adj[idx[x]].insert({idy[y], i});
            adj[idy[y]].insert({idx[x], i});
        }

        vector<int> vis(n * 4 + 1);
        vector<pair<int, int>> ans;
        auto dfs = [&](auto &dfs, int cur) -> int
        {
            vis[cur] = 1;
            int ret = 0;
            for (auto &[to, id] : adj[cur])
            {
                adj[to].erase({cur, id});
                if (!vis[to])
                {
                    int tmp = dfs(dfs, to);
                    if (tmp)
                        ans.push_back({tmp, id});
                    else if (ret)
                    {
                        ans.push_back({ret, id});
                        ret = 0;
                    }
                    else
                        ret = id;
                }
                else
                {
                    int tmp = 0;
                    if (tmp)
                        ans.push_back({tmp, id});
                    else if (ret)
                    {
                        ans.push_back({ret, id});
                        ret = 0;
                    }
                    else
                        ret = id;
                }
            }
            return ret;
        };
        for (int i = 1; i <= tot; i++)
            if (!vis[i])
                dfs(dfs, i);

        cout << ans.size() << '\n';
        vis.assign(n * 4 + 1, 0);
        for (auto &[x, y] : ans)
        {
            vis[x] = vis[y] = 1;
            cout << x << ' ' << y << '\n';
        }
        for (int i = 1, j = 0; i <= n * 2; i++)
        {
            if (vis[i])
                continue;
            j += 1;
            cout << i << " \n"[j % 2 == 0];
        }
    }
}
/*
3
 2
 0 0
 0 1
 1 0
 1 1
 2
 0 0
 0 1
 0 2
 0 3
 2
 0 0
 1 1
 2 2
 3 3
*/