#include <bits/stdc++.h>
#define endl '\n'
using namespace std;
using ll = long long;
using pii = pair<int, int>;
void solve()
{
    int n, k, mx = 0, rt = 1;
    cin >> n >> k;
    vector<int> p(n + 1);
    vector<int> cnt(n + 1, 0);
    vector<pii> seg(k + 1);
    for (int i = 1; i <= k; i++)
    {
        cin >> seg[i].first >> seg[i].second;
        for (int j = seg[i].first + 1; j <= seg[i].second; j++)
            p[j] = j - 1;
        cnt[seg[i].second - seg[i].first + 1]++;
        mx = max(mx, seg[i].second - seg[i].first + 1);
        if (seg[i].second - seg[i].first + 1 == mx)
            rt = seg[i].first;
    }
    for (int i = 1; i <= k; i++)
    {
        if (seg[i].second - seg[i].first + 1 == mx - 1 && seg[i].second - seg[i].first + 1 > 1)
        {
            cout << "IMPOSSIBLE" << endl;
            return;
        }
    }
    if (cnt[mx] >= 2)
        cout << "IMPOSSIBLE" << endl;
    else
    {
        for (int i = 1; i <= k; i++)
            if (seg[i].first != rt)
                p[seg[i].first] = rt;
        for (int i = 1; i <= n; i++)
            cout << p[i] << " ";
        cout << endl;
    }
}

int main()
{
#ifdef x3ea
    freopen("in.txt", "r", stdin);
#endif
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    int _ = 1;
    cin >> _;
    for (; _; _--)
        solve();
    return 0;
}