#include <bits/stdc++.h>
#ifdef LOCAL
#include "debug.h"
#else
#define deb(...)
#endif
using namespace std;
#define ll long long
// #define int long long
#define ull unsigned long long
#define pii pair<int, int>
#define db double
#define baoliu(x, y) cout << fixed << setprecision(y) << x
#define endl "\n"
#define alls(x) (x).begin(), (x).end()
#define fs first
#define sec second
#define bug(x) cerr << #x << " = " << x << endl
const int N = 2e5 + 10;
const int M = 1e6 + 10;
const int inf = 0x3f3f3f3f;
const int mod = 998244353;
const double eps = 1e-8;
const double PI = acos(-1.0);
void solve() {
    int n, k;
    cin >> n >> k;
    vector<pii> a(k + 1);
    for (int i = 1; i <= k; i++) cin >> a[i].fs >> a[i].sec;
    vector<int> len(k + 1);
    for (int i = 1; i <= k; i++) len[i] = a[i].sec - a[i].fs;
    deb(len);
    vector<int> p(n + 1);
    if (n == 1) {
        for (int i = 1; i <= n; i++) p[i] = i - 1;
        for (int i = 1; i <= n; i++) cout << p[i] << " ";
        cout << endl;
        return;
    }
    int mxpos = max_element(len.begin() + 1, len.end()) - len.begin();
    int mnpos = min_element(len.begin() + 1, len.end()) - len.begin();
    int mx = len[mxpos], mn = len[mnpos];
    int cnt = count(len.begin() + 1, len.end(), mx);
    deb(mx, mn, cnt);
    auto mkchain = [&](int hrt, int l, int r) {
        p[l] = hrt;
        for (int i = l + 1; i <= r; i++) p[i] = i - 1;
    };
    if (mx == mn) {
        cout << "IMPOSSIBLE" << endl;
    } else if (mx - mn == 1 && cnt >= 2) {
        cout << "IMPOSSIBLE" << endl;
    } else {
        if (cnt == 1) {
            int rt = a[mxpos].fs;
            mkchain(0, a[mxpos].fs, a[mxpos].sec);
            for (int i = 1; i <= k; i++) {
                if (i == mxpos)
                    continue;
                mkchain(rt, a[i].fs, a[i].sec);
            }
        } else {
            assert(mx - mn >= 2);
            int rt = a[mxpos].fs;
            mkchain(0, a[mxpos].fs, a[mxpos].sec);
            mkchain(rt + 1, a[mnpos].fs, a[mnpos].sec);
            for (int i = 1; i <= k; i++) {
                if (i == mxpos || i == mnpos)
                    continue;
                mkchain(rt, a[i].fs, a[i].sec);
            }
        }
        for (int i = 1; i <= n; i++) cout << p[i] << " ";
        cout << endl;
    }
}
signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
#ifdef LOCAL
    double starttime = clock();
    // freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
#endif
    int t = 1;
    cin >> t;
    while (t--) solve();
#ifdef LOCAL
    double endtime = clock();
    cerr << "Time Used: " << (double)(endtime - starttime) / CLOCKS_PER_SEC * 1000 << " ms" << endl;
#endif
    return 0;
}