#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


int N, K;
vector<int> L, R;

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%d%d", &N, &K);
    L.resize(K);
    R.resize(K);
    for (int k = 0; k < K; ++k) {
      scanf("%d%d", &L[k], &R[k]);
      --L[k];
    }
    
    vector<pair<int, int>> aks(K);
    for (int k = 0; k < K; ++k) {
      aks[k] = make_pair(R[k] - L[k], k);
    }
    sort(aks.begin(), aks.end(), greater<pair<int, int>>{});
    
    vector<int> par(N, -1);
    for (int k = 0; k < K; ++k) {
      for (int u = L[k] + 1; u < R[k]; ++u) {
        par[u] = u - 1;
      }
    }
    const int k0 = aks[0].second;
    for (int i = 1; i < K; ++i) {
      const int k = aks[i].second;
      par[L[k]] = L[k0];
    }
    
    if (K == 1 || aks[0].first > aks[1].first) {
      // OK
    } else if (aks[0].first - 2 >= aks[K - 1].first) {
      const int k = aks[K - 1].second;
      par[L[k]] = L[k0] + 1;
    } else {
      puts("IMPOSSIBLE");
      goto failed;
    }
    
    for (int u = 0; u < N; ++u) {
      if (u) printf(" ");
      printf("%d", par[u] + 1);
    }
    puts("");
   failed:{}
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}