#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<int, int> pii;



void solve() {
    int n, k;
    cin >> n >> k;
    int maxn = 0;
    std::vector<pii> a(k + 1);
    for(int i = 1; i <= k; i ++ ) {
        cin >> a[i].first >> a[i].second;
        maxn = max(maxn, a[i].second - a[i].first + 1);
    }
    int cnt = 0;
    int l = 0, r = 0;
    vector<int> f(n + 1);
    vector<int> hi(n + 1);
    for(int i = 1; i <= k; i ++ ) {
        if(a[i].second - a[i].first + 1 == maxn) {
            cnt ++ ;
            l = a[i].first, r = a[i].second;
            f[l] = 0;
            for(int j = l + 1; j <= r; j ++ ) {
                f[j] = j - 1;
            }
            for(int i = 1; i <= r - l; i ++ ) {
                hi[i] = r - i;
            }
        }
        if(cnt > 1) {
            cout << "IMPOSSIBLE";
            return ;
        }
    }
    for(int i = 1; i <= k; i ++ ) {
        if(a[i].first != l && a[i].second != r) {
            for(int j = a[i].first + 1; j <= a[i].second; j ++ ) {
                f[j] = j - 1;
            }
            f[a[i].first] = hi[a[i].second - a[i].first + 1];
        }
    }
    for(int i = 1; i <= n; i ++ ) {
        cout << f[i] << ' ';
    }
    cout << '\n';
}

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