#include <bits/stdc++.h>
#define int long long
#define endl '\n'
using namespace std;
typedef pair<int, int> PII;
const int inf = 2e18;

bool cmp(const PII &x, const PII &y)
{
    return x.second - x.first + 1 > y.second - y.first + 1;
}

void solves()
{
    int n, k;
    cin >> n >> k;
    vector<PII> e;
    for (int i = 0; i < k; i++)
    {
        int a, b;
        cin >> a >> b;
        e.push_back({a, b});
    }

    sort(e.begin(), e.end(), cmp);

    // for(auto item:e)
    //     cout<<item.first<<' '<<item.second<<endl;

    vector<int> fa(n + 10, 0);

    if (k == 1)
    {
        for (int i = e[0].first - 1; i <= e[0].second - 1; i++)
            cout << i << ' ';
        cout << endl;
        return;
    }

    int mx = e[0].second - e[0].first + 1;
    int mxc = e[1].second - e[1].first + 1;

    if (mx == mxc)
    {
        cout << "IMPOSSIBLE" << endl;
        return;
    }

    int root = e[0].first;
    for (auto item : e)
    {
        int l = item.first, r = item.second;
        for (int i = l; i <= r; i++)
        {
            if (i == l)
                fa[i] = root;
            else
                fa[i] = i - 1;
        }
    }

    for (int i = 1; i <= n; i++)
    {
        if (i == root)
            cout << 0 << ' ';
        else
            cout << fa[i] << ' ';
    }
    cout << endl;
}

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