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

bool cmp(pair<int, int> p1, pair<int, int> p2) {
  return (p1.second - p1.first + 1) > (p2.second - p2.first + 1);
}

int main() {
  int tt;
  cin >> tt;
  while (tt--) {
    int n, m;
    cin >> n >> m;
    pair<int, int> arr[m];
    for (int i=0; i<m; i++) {
      int l, r;
      cin >> l >> r;
      arr[i] = {l, r};
    }
    sort(arr, arr + m);
    if (arr[0].first != 1 || arr[m - 1].second != n) cout << "IMPOSSIBLE\n";
    else {
      bool ok = true;
      for (int i=1; i<m; i++) {
        if (arr[i - 1].second + 1 != arr[i].first) {
          ok = false;
          break;
        }
      }
      if (!ok) cout << "IMPOSSIBLE\n";
      else {
        sort(arr, arr + m, cmp);
        if (arr[0].second - arr[0].first + 1 == arr[m - 1].second - arr[m - 1].first + 1) cout << "IMPOSSIBLE\n";
        else if (arr[0].second - arr[0].first + 1 == arr[1].second - arr[1].first + 1) {
          if (arr[0].second - arr[0].first + 1 >= arr[m - 1].second - arr[m - 1].first + 1 + 2) {
            int sol[n + 1];
            for (int i=0; i<=n; i++) sol[i] = 0;
            for (int i=0; i<m; i++) {
              auto [l, r] = arr[i];
              if (i == m - 1) sol[l] = arr[0].first + 1;
              else if (i > 0) sol[l] = arr[0].first;
              else sol[l] = 0;
              for (int j=l+1; j<=r; j++) sol[j] = j - 1;
            }
            for  (int i=1; i<=n; i++) cout << sol[i] << " ";
            cout << "\n";
          }
          else cout << "IMPOSSIBLE\n";
        }
        else {
          int sol[n + 1];
          for (int i=0; i<=n; i++) sol[i] = 0;
          for (int i=0; i<m; i++) {
            auto [l, r] = arr[i];
            if (i > 0) sol[l] = arr[0].first;
            for (int j=l+1; j<=r; j++) sol[j] = j - 1;
          }
          for  (int i=1; i<=n; i++) cout << sol[i] << " ";
          cout << "\n";
        }
      }
    }
  }
}