#include<bits/stdc++.h>
using namespace std;
// #define int long long
#define debug(x) cout<<x<<"--------------------------------------\n" ;
const int N = 1e5 + 10;
typedef long long ll;
const int INF = 1e9;
const int MOD = 1e9 + 7;
typedef pair<int, int> PII;

int gcd(int a, int b) {
    return b ? gcd(b, a % b) : a;
}

ll qpow(int a, int k) {
    ll res = 1;
    while (k) {
        if (k & 1) res = 1ll * res * a % MOD;
        a = 1ll * a * a % MOD;
        k >>= 1;
    }
    return res;
}

int n, m, k;
string s;

void solve() {
    cin >> n >> k;
    vector<PII> seg(k + 1);
    for (int i = 1; i <= k; i++) {
        cin >> seg[i].first >> seg[i].second;
    }
    sort(seg.begin() + 1, seg.end(), [&](PII a, PII b) {
        return (a.second - a.first) > (b.second - b.first);
    });
    if (!(seg[k].second - seg[k].first <= seg[1].second - seg[1].first - 1)) {
        cout << "IMPOSSIBLE\n";
        return;
    }
    int mx = seg[1].second - seg[1].first;
    // vector<vector<int>> pos(mx+1);
    vector<int> fa(n + 1);
    bool f = 0;
    for (int i = 1; i <= k - 1; i++) {
        // debug(i)
        int len = seg[i].second - seg[i].first + 1;
        if (i == 1) {
            fa[seg[1].first] = 0;
        } else {
            if (len == seg[1].second - seg[1].first + 1) {
                f = 1;
            }
            fa[seg[i].first] = seg[1].first;
        }
        for (int j = seg[i].first + 1; j <= seg[i].second; j++) {
            fa[j] = j - 1;
        }
    }
    if (f) {
        fa[seg[k].first] = seg[1].first + 1;
        for (int j = seg[k].first + 1; j <= seg[k].second; j++) {
            fa[j] = j - 1;
        }
    } else {
        fa[seg[k].first] = seg[1].first;
        for (int j = seg[k].first + 1; j <= seg[k].second; j++) {
            fa[j] = j - 1;
        }
    }

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

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int tt = 1;
    cin >> tt;
    while (tt--) solve();
    return 0;
}