#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
using pii = pair<int, int>;
constexpr int maxn = 100000 + 10;
pii p[maxn];
int a[maxn];
void solve()
{
    int n, k;
    cin >> n >> k;
    for (int i=1;i<=k;++i) cin >> p[i].first >> p[i].second;
    sort(p + 1, p + k + 1, [](pii x, pii y) {return x.second - x.first > y.second - y.first;});
    if (p[1].second - p[1].first == p[k].second - p[k].first) return cout << "IMPOSSIBLE\n", void();
    if (p[1].second - p[1].first == p[k].second - p[k].first + 1 && p[1].second - p[1].first == p[2].second - p[2].first) return cout << "IMPOSSIBLE\n", void();
    for (int i=1;i<=k;++i)
        for (int j=p[i].first+1;j<=p[i].second;++j) a[j] = j - 1;
    a[p[1].first] = 0;
    for (int i=2;i<=k;++i)
        if (p[i].second - p[i].first >= p[1].second - p[1].first - 1)
            a[p[i].first] = p[1].first;
        else a[p[i].first] = p[1].first + 1;
    for (int i=1;i<=n;++i) cout << a[i] << ' ';
    cout << '\n';
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while (t--) solve();
    return 0;
}