#include<bits/stdc++.h>

using namespace std;   

#define forn(i, n) for(int i = 0; i < int(n); i++)
#define fore(i, l, r) for(int i = int(l); i < int(r); i++)
#define sz(a) int((a).size())

typedef long long li;

int n, k;
vector<pair<int, int>> a;

bool read() {
	if (!(cin >> n >> k))
		return false;
	a.resize(k);
	forn(i, k){
		cin >> a[i].first >> a[i].second;
		--a[i].first, --a[i].second;
	}
	return true;
}

void solve() {
	sort(a.begin(), a.end(), [](const pair<int, int> &a, const pair<int, int> &b){
		return a.second - a.first < b.second - b.first;
	});
	vector<int> cnt(n + 1);
	for (auto [l, r] : a) cnt[r - l + 1]++;
	if (k > 1 && a.back().second - a.back().first == 1 && cnt[2] >= 2){
		cout << "IMPOSSIBLE\n";
		return;
	}
	if (k > 1 && a[0].second - a[0].first == a.back().second - a.back().first){
		cout << "IMPOSSIBLE\n";
		return;
	}
	vector<int> p(n, -1);
	forn(i, k) fore(j, a[i].first, a[i].second)
		p[j + 1] = j;
	forn(i, k - 1)
		p[a[i].first] = max(a.back().first, a.back().second - (a[i].second - a[i].first + 1));
	//for (auto [l, r] : a)
	//	cerr << l + 1 << " " << r + 1 << "  ";
	//cerr << endl;
	//forn(i, n) if (p[i] != -1)
	//	cerr << p[i] + 1 << " " << i + 1 << endl;
	forn(i, n)
		cout << p[i] + 1 << " ";
	cout << '\n';
}

int main() {
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
#endif
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	
	int t = 1;
	cin >> t;
	forn(i, t) {
	 	read();
		solve();
	}
}