#include <bits/stdc++.h>

using i64 = long long;

void solve() {
    int n, k;
    std::cin >> n >> k;
    std::vector<int> f(n, -1);
    std::vector<int> init(n);
    std::vector<std::array<int, 2>> pa(k);
    for (int i = 0; i < k; i++) {
        int l, r;
        std::cin >> l >> r;
        l--, r--;
        for (int j = l; j <= r; j++) {
            if (j < r) f[j + 1] = j;
            init[j] = r - j + 1;
        }
        pa[i] = {r - l + 1, l};
    }

    std::sort(pa.begin(), pa.end());
    
    if (k == 1) {
        for (int i = 0; i < n; i++) {
            std::cout << f[i] + 1 << " \n"[i == n - 1];
        }
        return;
    }
    if (pa[0][0] == pa.back()[0]) {
        std::cout << "IMPOSSIBLE\n";
        return;
    }

    std::vector<int> vx;
    for (int i = 0; i < pa.back()[0]; i++) {
        vx.push_back(pa.back()[1] + i);
    }
    std::reverse(vx.begin(), vx.end());
    pa.pop_back();
    int p = 0;
    for (auto [len, top] : pa) {
        while (len >= init[vx[p]]) {
            p++; 
        }
        f[top] = vx[p];
    }
    for (int i = 0; i < n; i++) {
        std::cout << f[i] + 1 << " \n"[i == n - 1];
    }
}
int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int t;
    std::cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}