#include <bits/stdc++.h>

using i64 = long long;

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

    std::vector<int> l(k), r(k);
    int cnt = 0;
    for (int i = 0; i < k; i++) {
        std::cin >> l[i] >> r[i];
        l[i]--;
        cnt += r[i] - l[i] - 1;
    }
    if (cnt + k - 1 != n - 1) {
        //std::cerr << "debug\n";
        std::cout << "IMPOSSIBLE\n";
        return;
    }
    std::vector<std::vector<int>> adj(n);
    for (int i = 0; i < k; i++) {
        for (int j = l[i]; j + 1 < r[i]; j++) {
            adj[j].push_back(j + 1);
        }
    }

    std::vector<int> p(k);
    std::iota(p.begin(), p.end(), 0);
    std::sort(p.begin(), p.end(), [&](int i, int j) {
        return r[i] - l[i] > r[j] - l[j];
    });

    int rt = l[p[0]];
    std::vector<int> top(n, -1), ans(n, -1), parent(n);
    for (int i = 1; i < k; i++) {
        adj[rt].push_back(l[p[i]]);
    }
    ans[rt] = rt;
    for (int i = 0; i < k; i++) {
        for (int j = l[i]; j < r[i]; j++) {
            ans[j] = l[i];
        }
    }

    if (std::find(ans.begin(), ans.end(), -1) != ans.end()) {
        std::cout << "IMPOSSIBLE\n";
        return;
    }
    parent[rt] = -1;
    top[rt] = rt;
    //std::cerr << rt << "\n";

    auto dfs = [&](auto &&self, int u) -> void {
        for (auto v : adj[u]) {
            parent[v] = u;
            top[v] = v == adj[u][0] ? top[u] : v;
            self(self, v);
        }
    };
    dfs(dfs, rt);

    if (ans != top) {
        std::cout << "IMPOSSIBLE\n";
        return;
    }

    for (int i = 0; i < n; i++) {
        std::cout << parent[i] + 1 << " \n"[i == n - 1];
    }
}

int main() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);

    int t;
    std::cin >> t;

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