#include<bits/stdc++.h>
using namespace std;
using ll=long long;
#define pii pair<int, int>

void work()
{
    int n, k; cin >> n >> k;
    vector<pii > a(k + 1);
    vector<int> f(n + 1);
    for(int i = 1; i <= k; i++){
        cin >> a[i].first >> a[i].second;
        for(int j = a[i].first + 1; j <= a[i].second; j++)
            f[j] = j - 1;
    }
    auto cmp =[](pii x, pii y) -> bool{
        return x.second - x.first > y.second - y.first;
    };
    sort(a.begin() + 1, a.end(), cmp);
    int mxlen = a[1].second - a[1].first;
    int p = 2, x = a[1].first;
    for(int i = mxlen; i >= 0; i--){
        if(a[p].second - a[p].first < i){
            for(int j = p; j <= k; j++)
                f[a[j].first] = x;
            break;
        }
        while(p <= k && a[p].second - a[p].first == i){
            f[a[p].first] = x;
            p++;
        }
        if(p > k){        
            cout <<"IMPOSSIBLE\n";
            return;
        }
        x++;
    }
    for(int i = 1; i <= n; i++)
        cout << f[i]<<" ";
    cout <<"\n";
    /*if(a[1].second - a[1].first == a[2].second - a[2].first) {
        cout <<"IMPOSSIBLE\n";
        return;
    }
    int rt = a[1].first;
    for(int i = 1; i <= n; i++){
        if(i == rt) cout <<"0 ";
        else{
            if(!f[i]) cout << rt<<" ";
            else cout << f[i]<<" ";
        }
    }
    cout <<"\n";*/
}

int main()
{
    std::cin.tie(0);
    std::cin.sync_with_stdio(0);
    int t=1;
    std::cin>>t;
    while(t--)
        work();
    return 0;
}
/*
4
12 5
1 5
9 11
7 8
6 6
12 12
4 3
1 1
4 4
2 3
2 2
1 1
2 2
17 6
14 17
1 4
5 8
9 11
12 12
13 13
*/
/*
1
17 6
14 17
1 4
5 8
9 11
12 12
13 13
*/