#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, l, r) for (int i = l; i <= r; i++)
const int N = 1e5 + 10;
int n, k;
struct node
{
    int l, r, len;
    bool operator<(const node &a) const { return len > a.len; }
} a[N];
int ans[N];
void solve()
{
    cin >> n >> k;
    rep(i, 1, k)
    {
        cin >> a[i].l >> a[i].r;
        a[i].len = a[i].r - a[i].l + 1;
    }
    sort(a + 1, a + 1 + k);
    if (a[1].len > a[2].len)
    {
        rep(i, 1, k)
        {
            rep(j, a[i].l + 1, a[i].r)
            {
                ans[j] = j - 1;
            }
            if (i != 1)
                ans[a[i].l] = a[1].l;
        }
    }
    else
    {

        rep(i, 1, k)
        {
            rep(j, a[i].l + 1, a[i].r)
            {
                ans[j] = j - 1;
            }
            if (i != 1 && i != k)
                ans[a[i].l] = a[1].l;
        }
        if (a[k].len > a[1].len - 2)
        {
            return cout << "IMPOSSIBLE" << endl, void();
        }
        int j, cnt;
        for (j = a[1].r, cnt = 1; cnt <= a[k].len; j--, cnt++)
            ;
        ans[a[k].l] = j;
    }
    ans[a[1].l] = 0;
    rep(i, 1, n) cout << ans[i] << " ";
    cout << endl;
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    cin >> t;
    while (t--)
        solve();
    return 0;
}