#include <bits/stdc++.h>

using namespace std;

struct node {
    int l, r, len;
};

bool cmp(node a, node b) {
    return a.len > b.len;
}

string noans = "IMPOSSIBLE";

const int maxn = 2e5 + 100;

int root[maxn], ans[maxn];
node segment[maxn];

void solve() {
    int n, k;
    cin >> n >> k;
    for (int i = 0; i <= n + 1; ++i)
        ans[i] = 0, root[i] = 0, segment[i].l = segment[i].r = segment[i].len = 0;
    for (int i = 1; i <= k; ++i) {
        cin >> segment[i].l >> segment[i].r;
        segment[i].len = segment[i].r - segment[i].l + 1;
    }
    sort(segment + 1, segment + 1 + k, cmp);

    int maxlen = segment[1].len;
    if (k >= 2 && segment[2].len == maxlen) {
        cout << noans << "\n";
        return;
    }

    int len = segment[1].len;
    for (int i = segment[1].l, temp = 1; i <= segment[1].r; ++i) {
        if (i == segment[1].l)
            ans[i] = 0;
        else
            ans[i] = i - 1;
        root[len - temp] = i;
        temp++;
    }

    for (int i = 1; i <= k; ++i) {
        for (int j = segment[i].l; j <= segment[i].r; j++) {
            if (j == segment[i].l)
                ans[j] = root[segment[i].len];
            else
                ans[j] = j - 1;
        }
    }

    for (int i = 1; i <= n; ++i)
        cout << ans[i] << " \n"[i == n];
    return;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}