#include <algorithm>
#include <iostream>
#include <map>
#include <set>
#include <vector>
using namespace std;
using ll = long long;
// using pii = pair<int, int>;
struct item {
    int l, r;
};
void solve() {
    int n, k;
    cin >> n >> k;
    vector<int> p(n + 1);
    vector<item> a(k);
    for (int i = 0; i < k; ++i) {
        cin >> a[i].l >> a[i].r;
        for (int j = a[i].l + 1; j <= a[i].r; ++j) {
            p[j] = j - 1;
        }
    }
    sort(a.begin(), a.end(), [](const item& a, const item& b) { return a.r - a.l > b.r - b.l; });
    if (k == 1) {
        for (int i = 1; i <= n; ++i) cout << i - 1 << " ";
        cout << '\n';
        return;
    }
    if (a[0].r - a[0].l == a.back().r - a.back().l) {
        cout << "IMPOSSIBLE" << '\n';
        return;
    }
    if (a[0].r - a[0].l == 1) {
        for (int i = 1; i < a.size(); ++i) {
            if (a[i].r - a[i].l == 1) {
                cout << "IMPOSSIBLE" << '\n';
                return;
            }
        }
        for (int i = 1; i <= n; ++i) cout << (i == a[0].l ? 0 : a[0].l) << " ";
        cout << '\n';
        return;
    }
    p[a[0].l] = 0;
    p[a.back().l] = a[0].l + 1;
    for (int i = 1; i < a.size(); ++i) {
        if (i == a.size() - 1) continue;
        p[a[i].l] = a[0].l;
    }
    for (int i = 1; i <= n; ++i) cout << p[i] << " ";
    cout << '\n';
    return;
}
int main() {
    cin.tie(0), cout.tie(0), ios::sync_with_stdio(0);
    int t;
    cin >> t;
    while (t--) solve();
}
/*
1
3 1
1 3

3
12 5
1 5
9 11
7 8
6 6
12 12
4 3
1 1
4 4
2 3
2 2
1 1
2 2
*/