#include <bits/stdc++.h>
using namespace std;
#define vv vector
#define ll long long
const int N = 200000 + 5;
const int P = 1e9 + 7;
const ll inf = 1e18;

mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count());
uniform_int_distribution<ll> rd(0, 1e9);
inline ll rnd() { return rd(gen); }

void qfl_zzz()
{
    ll n, k;
    cin >> n >> k;
    vv<ll> fa(n + 1), sz(n + 1);
    vv<vv<ll>> a(k + 1);
    for (ll i = 1; i <= k; ++i)
    {
        ll l, r;
        cin >> l >> r;
        for (ll j = l; j <= r; ++j)
        {
            a[i].push_back(j);
            if (j > l)
                fa[j] = j - 1;
        }
    }
    sort(a.begin() + 1, a.end(), [&](auto x, auto y)
         { return x.size() > y.size(); });

    ll i = a[1].back(), j = k;
    for (; i > 0 && j >= 2; i = fa[i])
    {
        while (j >= 2 && sz[i] >= a[j].size())
        {
            fa[*a[j].begin()] = i;
            sz[i] += a[j].size();
            --j;
        }
        ++sz[i], sz[fa[i]] += sz[i];
    }

    if (j >= 2)
    {
        cout << "IMPOSSIBLE\n";
        return;
    }

    for (ll i = 1; i <= n; ++i)
        cout << fa[i] << " \n"[i == n];
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    srand(unsigned(time(0)));
    cout << setiosflags(ios::fixed) << setprecision(12);

#ifdef LOCAL
    freopen("in.txt", "r", stdin);
    freopen("std.txt", "w", stdout);
#endif

    int T = 1;
    cin >> T;
    while (T--)
        qfl_zzz();

    return 0;
}