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

void solve(){
    int N,K;
    cin >> N >> K;
    vector<pair<int,int>> P(K);
    int longest = 0;
    bool tie = false;
    for(int i = 0; i < K; i++){
        cin >> P[i].first >> P[i].second;
        if(i > 0){
            if(P[longest].second - P[longest].first < P[i].second - P[i].first){
                longest = i;
                tie = false;
            }else if(P[longest].second - P[longest].first == P[i].second - P[i].first){
                tie = true;
            }
        }
        
    }
    if(N == 1){
        cout << 0 << endl;
        return;
    }
    if(P[longest].first == P[longest].second || tie){
        cout << "IMPOSSIBLE" << endl;
        return;
    }
    int R = 0;
    R = P[longest].first;
    vector<int> ans(N);
    for(int i = 0; i < K; i++){
        if(P[i].first == R){
            ans[P[i].first - 1] = 0;
        }else{
            ans[P[i].first - 1] = R;
        }
        for(int j = P[i].first + 1; j <= P[i].second; j++){
            ans[j - 1] = j - 1;
        }
    }
    for(int i = 0; i < N; i++)cout << ans[i] << " \n"[i == N-1];
}

int main(){
    cin.tie(0) -> sync_with_stdio(0);
    int T;
    cin >> T;
    while(T--){
        solve();
    }
    return 0;
}