#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
typedef long long ll;
#define debug(x) cout<<#x<<": "<<x<<endl
#define rep(i, a, b) for(int i = (a); i <= (b); i++)
#define per(i, a, b) for(int i = (a); i >= (b); i--)
#define sz(a) a.size()
#define all(a) a.begin(),a.end()
typedef pair<ll, ll> pll;
const ll N = 3e5 + 10;

void solve()
{
    ll n, m;
    cin >> n >> m;
    ll fa[n + 5];
    vector<pll>ve;
    rep(i, 1, n) {
        fa[i] = 0;
    }
    rep(i, 1, m) {
        ll l, r;
        cin >> l >> r;
        ve.push_back({-1 * (r - l + 1), l});
        per(j, r, l + 1) {
            fa[j] = j - 1;
        }
    }
    if(m == 1) {
        rep(i, 1, n) {
            cout << fa[i] << " \n"[i == n];
        }
    }
    else {
        sort(all(ve));
        rep(i, 1, sz(ve) - 1) {
            fa[ve[i].second] = ve[0].second;
        }
        if(ve[0].first == -1 || ve.back().first < 2 + ve[0].first) {
            cout << "IMPOSSIBLE" << endl;
            return;
        }
        if(ve[0].first == ve[1].first) fa[ve.back().second] = ve[0].second + 1;
        rep(i, 1, n) {
            cout << fa[i] << " \n"[i == n];
        }
    }
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    int T=1;
    cin>>T;
    while(T--)
    {
        solve();
    }
    return 0;
}