//
// Created by Zhangfenglai 24-11-15
// 下午4:55
#include <bits/stdc++.h>
#define dg(x) cout << #x << " = " << x << '\n'
#define int long long
using namespace std;
typedef long long ll;
constexpr int maxN = 2e5 + 5;
constexpr int inf = 0x3f3f3f3f;
constexpr ll INF = 0x3f3f3f3f3f3f3f3f;

struct chain{
    int l, r;
    int len;

    bool operator<(const chain &b) const{
        return len > b.len;
    }
};

void solve(){
    int n, k;
    cin >> n >> k;
    vector<chain> ch(k + 1);
    vector<int> fa(n + 1);
    for(int i = 1; i <= k; i++) {
        cin >> ch[i].l >> ch[i].r;
        ch[i].len = ch[i].r - ch[i].l + 1;
        for(int j = ch[i].l + 1; j <= ch[i].r; j++) {
            fa[j] = j - 1;
        }
    }
    sort(ch.begin() + 1, ch.end());
    chain mx = ch[1];
    chain mn = ch.back();
    if(mx.len == 2) {
        for(int i = 2; i <= k; i++) {
            if(ch[i].len >= mx.len) {
                cout << "IMPOSSIBLE" << '\n';
                return;
            }
            fa[ch[i].l] = mx.l;
        }
        for(int i = 1; i <= n; i++) {
            cout << fa[i] << ' ';
        }
        cout << '\n';
        return;
    }
    if(mx.len <= mn.len) {
        cout << "IMPOSSIBLE" << '\n';
        return;
    }
    fa[mn.l] = mx.l + 1;
    for(int i = 2; i <= k - 1; i++) {
        fa[ch[i].l] = mx.l;
    }
    for(int i = 1; i <= n; i++) {
        cout << fa[i] << ' ';
    }
    cout << '\n';
}

int32_t main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int t;
    cin >> t;
    //t = 1;
    while(t--)solve();
    return 0;
}