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

#define int long long

constexpr int inf = 1e18;

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

    vector<int> fa(n + 1);
    vector<int> l(k + 1), r(k + 1);
    int mx = 0, mn = inf;
    for (int i = 1; i <= k; i++) {
        cin >> l[i] >> r[i];
        for (int j = l[i] + 1; j <= r[i]; j++) {
            fa[j] = j - 1;
        }
        int len = r[i] - l[i] + 1;
        if (len > r[mx] - l[mx] + 1) {
            mx = i;
        }
        if (mn == inf || len < r[mn] - l[mn] + 1) {
            mn = i;
        }
    }

    if (r[mn] - l[mn] == r[mx] - l[mx]) {
        cout << "IMPOSSIBLE\n";
        return;
    }

    if (r[mn] - l[mn] == r[mx] - l[mx] - 1) {
        for (int i = 1; i <= k; i++) {
            if (i == mx) continue;
            int len = r[i] - l[i] + 1;
            if (len == r[mx] - l[mx] + 1) {
                cout << "IMPOSSIBLE\n";
                return;
            }
        }
    }

    for (int i = 1; i <= k; i++) {
        if (i == mx) continue;
        int len = r[i] - l[i] + 1;
        fa[l[i]] = max(l[mx], r[mx] - len);
    }

    for (int i = 1; i <= n; i++) {
        cout << fa[i] << " \n"[i == n];
    }

}

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

    int t = 1;
    cin >> t;

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

    return 0;
}