#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using PII = pair<int,int>;

void solve() {

	int n,k;
	cin >> n >> k;

	vector<pair<int,int>> seg(k);
	for (int i = 0 ; i < k ; ++i) {
		cin >> seg[i].first >> seg[i].second;
	}

	auto getlen = [&] (PII x) {
		return x.second - x.first + 1;
	};
	sort(seg.begin() , seg.end() , [&](PII x , PII y){
		return getlen(x) > getlen(y);
	});
	
	if (k == 1) {
		for (int i = 1 ; i <= n ; ++i) {
			cout << i - 1 << " \n"[i == n];
		}
		return;
	}
	if (n == 1) {
		cout << 0 << "\n";
		return;
	}

	vector<int> par(n + 1);
	for (int j = 0 ; j < k ; ++j) {
		for (int i = seg[j].first ; i <= seg[j].second ; ++i) {
			if (i != seg[j].first) par[i] = i - 1;
		}	
	}
		
	int id = 0;
	while (id < k && getlen(seg[id]) == getlen(seg[0])) {
		id ++;
	}
	if (id == k) {
		cout << "IMPOSSIBLE\n";
		return;
	}

	for (int j = id ; j < k ; ++j) {
		int i = seg[j].first;
		par[i] = seg[0].first + 1;
	}

	for (int j = 1 ; j < id ; ++j) {
		int i = seg[j].first;
		par[i] = seg[0].first;
	}

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

int main() {
	
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int t = 1;
	cin >> t;
	while (t--) {
		solve();
	}

	return 0;
}