#include <bits/stdc++.h>
using namespace std;
#define int long long
int n, k;
const int maxn = 1e5 + 10;
pair<int, int> a[maxn];
int fa[maxn];
void solve()
{
    cin >> n >> k;
    for (int i = 1; i <= k; i++)
    {
        cin >> a[i].first >> a[i].second;
    }
    sort(a + 1, a + 1 + k, [](pair<int, int> &a, pair<int, int> &b)
         { return a.second - a.first > b.second - b.first; });
    map<int, int> mp;

    for (int i = 1; i <= k; i++)
    {
        if (i == 1)
        {
            for (int l = a[i].first; l <= a[i].second; l++)
            {
                if (l == a[i].first)
                {
                    fa[l] = 0;
                }
                else
                {
                    fa[l] = l - 1;
                }
            }
            int cnt = 0;
            for (int l = a[i].second; l >= a[i].first; l--)
            {
                mp[cnt] = l;
                cnt++;
            }
        }
        else
        {
            int cnt = 0;
            for (int l = a[i].first; l <= a[i].second; l++)
            {
                cnt++;
                if (l == a[i].first)
                {
                    fa[l] = 0;
                }
                else
                {
                    fa[l] = l - 1;
                }
            }
            auto p = mp.lower_bound(cnt);
            if (p == mp.end())
            {
                cout << "IMPOSSIBLE" << '\n';
                return;
            }
            else
            {
                fa[a[i].first] = p->second;
            }
        }
    }
    for (int i = 1; i <= n; i++)
        cout << fa[i] << ' ';
    cout << '\n';
}

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