#include <bits/stdc++.h>
using namespace std;
void solve() {
    int n, k;
    cin >> n >> k;

    vector<pair<int, int>> a(k);
    for (auto &[l, r] : a) {
        cin >> l >> r;
    }

    vector<int> sum(n + 2);
    for (auto &[l, r] : a) {
        sum[l]++;
        sum[r + 1]--;
    }

    for (int i = 1; i <= n; i++) {
        sum[i] += sum[i - 1];
        if (sum[i] != 1) {
            cout << "IMPOSSIBLE\n";
            return;
        }
    }

    int root = a[max_element(a.begin(), a.end(), [&](auto l, auto r) {
        return l.second - l.first < r.second - r.first;
    }) - a.begin()].first;

    if (k != 1) {
        int f = 0;
        for (int i = 1; i < k; i++) {
            if (a[i].second - a[i].first != a[0].second - a[0].first) {
                f = 1;
                break;
            }
        }
        if (!f) {
            if (n == 1) {
                cout << "0\n";
            } else {
                cout << "IMPOSSIBLE\n";
            }
            return;
        }
    }

    vector<int> fa(n + 1);
    for (auto &[l, r] : a) {
        if (l != root) {
            fa[l] = root;
        }
        for (int i = l + 1; i <= r; i++) {
            fa[i] = i - 1;
        }
    }

    for (int i = 1; i <= n; i++) {
        cout << fa[i] << " \n"[i == n];
    }
}
int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    int TT;
    cin >> TT;

    while (TT--) {
        solve();   
    }
    return 0;
}