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

void solve(){
    int N,K;
    cin >> N >> K;
    vector<pair<int,int>> P(K);
    vector<pair<int,int>> L(K);

    for(int i = 0; i < K; i++){
        cin >> P[i].first >> P[i].second;
        L[i] = {P[i].second - P[i].first + 1, i};
        
    }
    sort(L.begin(), L.end());

    if(N == 1){
        cout << 0 << endl;
        return;
    }
    if(K == 1){
        for(int i = 0; i < N; i++){
            cout << i +1 << " \n"[i == N-1];
        }
        return;
    }
    if(L[K-1].first == L[K-2].first){
        if(L[K-1].first - 1 > L[0].first){
            vector<int> ans(N);
            for(int i = 0; i < K; i++){
                if(L[K-1].second == i){
                    ans[P[i].first - 1] = 0;
                }else if(L[0].second == i){
                    ans[P[i].first - 1] = P[L[K-1].second].first + 1;
                }else{
                    ans[P[i].first - 1] = P[L[K-1].second].first;
                }
                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];
        }else{
            cout << "IMPOSSIBLE" << "\n";
        }
        return;
    }

    int R = 0;
    R = P[L[K-1].second].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;
}