#include <bits/stdc++.h>
using i64 = long long;
void solve() {
    int n, k;
    std::cin >> n >> k;
    std::vector<int> p(n + 1);
    std::vector<std::array<int, 2>> ch(k);
    for (int i = 0; i < k; i++) {
        std::cin >> ch[i][0] >> ch[i][1];
        for (int j = ch[i][0] + 1; j <= ch[i][1]; j++) {
            p[j] = j - 1;
        }
    }
    std::sort(ch.begin(), ch.end(), [&](auto x, auto y) -> bool {
        return x[1] - x[0] > y[1] - y[0];
    });
    p[ch[0][0]] = 0;
    auto sz = [&](auto x) -> int {
        return x[1] - x[0] + 1;
    };
    int idx = ch[0][1] - 1, curr = 1, j = k - 1;
    while (idx >= ch[0][0] && j >= 1) {
        int tmp = 0;
        while (j >= 1 && idx >= ch[0][0] && curr >= sz(ch[j])) {
            p[ch[j][0]] = idx;
            tmp += sz(ch[j]);
            j--;
        }
        curr += tmp;
        while (j >= 1 && idx >= ch[0][0] && curr < sz(ch[j])) {
            idx--, curr++;
        }
    } 
    int cnt = 0;
    for (int i = 1; i <= n; i++) {
        cnt += p[i] == 0;
        if (cnt > 1) {
            std::cout << "IMPOSSIBLE" << '\n';
            return;
        }
    }
    for (int i = 1; i <= n; i++) {
        std::cout << p[i] << " \n"[i == n];
    }

}
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0), std::cout.tie(0);
    int t;
    std::cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}