#include <bits/stdc++.h>

#define int long long

using std::cin;
using std::cout;
using std::vector;
using std::string;
using std::endl;

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

    if(k == 1) {
        int l, r;
        cin >> l >> r;
        if(l == 1 and r == n) {
            for(int i = 1;i <= n; i++) {
                cout << i - 1 << " ";
            }

            cout << "\n";
            return;
        }else {
            cout << "IMPOSSIBLE\n";
            return;
        }
    }

    vector<int> l(k), r(k);
    for(int i = 0;i < k; i++) {
        cin >> l[i] >> r[i];
    }

    vector<int> p(k);
    std::iota(p.begin(), p.end(), 0LL);

    std::sort(p.begin(), p.end(), [&](int i, int j) {
        // if(r[i] - l[i] == r[j] - l[j]) {
        //     return (l[i] == l[j]) ? (r[i] < r[j]) : (l[i] < l[j]);
        // }
        return (r[i] - l[i]) > (r[j] - l[j]);
    });

    auto seg = [&](int i) {
        return r[i] - l[i];
    };

    if(seg(p[0]) == seg(p[1])) {
        cout << "IMPOSSIBLE\n";
        return;
    }

    vector<int> ans(n + 1);
    int root = -1;

    for(int j = 0;j < k; j++) {
        int i = p[j];
        if(j == 0) {
            ans[l[i]] = 0;
            root = l[i];
            for(int k = l[i] + 1;k <= r[i]; k++) {
                ans[k] = k - 1;
            }
        }else {
            ans[l[i]] = root;
            for(int k = l[i] + 1;k <= r[i]; k++) {
                ans[k] = k - 1;
            }
        }
    }

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

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int T;
    cin >> T;
    while(T--) {
        solve();
    }

    return 0;
}