#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;

#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define rep(i, n) for (int i = 0; i < (n); i += 1)
#define len(a) ((int)(a).size())

mt19937 rnd(234);
const ll inf = 1e18;

void solve() {
    int n, k;
    cin >> n >> k;

    vector<pair<int, int>> chains;
    for (int i = 0; i < k; ++i) {
        int l, r;
        cin >> l >> r;
        chains.push_back({l, r});
    }
    sort(rall(chains), [&](pair<int, int> a, pair<int, int> b) {
        return a.second - a.first < b.second - b.first;
    });
    if (chains[0].second - chains[0].first == 0 && n != 1) {
        cout << "IMPOSSIBLE\n";
        return;
    }

    vector<int> pars(n);
    int root = -1;
    for (int i = 0; i < chains.size(); ++i) {
        if (i == 0) {
            root = chains[i].first;
            int prev = root;
            for (int j = chains[i].first + 1; j <= chains[i].second; ++j) {
                pars[j - 1] = prev;
                prev = j;
            }
        } else {
            int prev = root;
            for (int j = chains[i].first; j <= chains[i].second; ++j) {
                pars[j - 1] = prev;
                prev = j;
            }
        }
    }

    for (auto c : pars)
        cout << c << " ";
    cout << "\n";
}

int32_t main() {
    if (1) {
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout.tie(0);
    }

    int t;
    cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}