#include <bits/stdc++.h>

#define X first
#define Y second
#define PB push_back

using namespace std;

const int N = 1e5 + 500;

int par[N], n, k;
vector < pair < int, int > > v;

void solve() {
	v.clear();
	scanf("%d%d", &n, &k);
	for(int i = 0;i < k;i++) {
		int l, r; scanf("%d%d", &l, &r);
		for(int i = l + 1;i <= r;i++) par[i] = i - 1;
		v.PB({r - l + 1, l});
	}
	sort(v.rbegin(), v.rend());
	if(k == 1 || v[0].X > v[1].X) {
		par[v[0].Y] = 0;
		for(int i = 1;i < k;i++)
			par[v[i].Y] = v[0].Y;
	} else if(v.back().X <= v[0].X - 2) {
		par[v.back().Y] = v[0].Y + 1;
		for(int i = 1;i + 1 < k;i++) {
			par[v[i].Y] = v[0].Y;
		}
	} else {
		printf("IMPOSSIBLE\n");
		return;
	}
	for(int i = 1;i <= n;i++)
		printf("%d ", par[i]);
	printf("\n");
}

int main() {
	int T; scanf("%d", &T);
	for(;T--;) solve();
	return 0;
}