#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 (getlen(seg[0]) == getlen(seg[1])) {
		cout << "IMPOSSIBLE\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;
		}	
	}

	vector<int> pos;
	for (int j = 1 ; j < k ; ++j) {
		pos.emplace_back(getlen(seg[j]));
	}
	sort(pos.begin() , pos.end());
	pos.erase(unique(pos.begin() , pos.end()) , pos.end());

	int m = pos.size();
	auto find = [&] (int x) {
		return lower_bound(pos.begin() , pos.end() , x) - pos.begin();
	};

	int sz = getlen(seg[0]);
	for (int j = 1 ; j < k ; ++j) {
		int i = seg[j].first , p =  m - 1 - find(getlen(seg[j]));
		if (p >= sz) {
			cout << "IMPOSSIBLE\n";
			return;
		} else {
			par[i] = seg[0].first + p;
		}
	}

	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;
}