#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <random>
#include <unordered_map>
#include <unordered_set>
#include <assert.h>
#include <climits>
#include <iomanip>
using namespace std;

void solve([[maybe_unused]] int t)
{
  int n, k;
  cin >> n >> k;
  vector<int> sol(n + 1);
  vector<pair<int, int>> v(k);
  for (auto &[l, r] : v)
  {
    cin >> l >> r;
    for (int i = l + 1; i <= r; i++)
    {
      sol[i] = i - 1;
    }
  }

  sort(v.begin(), v.end(), [](auto x, auto y)
       { return x.second - x.first > y.second - y.first; });

  int curr = v[0].first, len = v[0].second - v[0].first;

  bool ok = false || (k == 1);
  for (int i = 1; i < k; i++)
  {
    int x = v[i].second - v[i].first + 1;

    while (i < k && v[i].second - v[i].first + 1 == x)
    {
      sol[v[i].first] = curr;
      i++;
    }
    i--;

    if (x <= len)
    {
      ok = true;
    }

    curr++;
    len--;
  }

  if (!ok)
  {
    cout << "IMPOSSIBLE\n";
    return;
  }

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

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

  int n = 1;
  cin >> n;
  for (int i = 1; i <= n; i++)
    solve(i);
}