#include <bits/stdc++.h>
#define int long long
using namespace std;
pair<int,int>s[200010];
int p[200010];
bool cmp(pair<int,int>x,pair<int,int>y){
	return x.second-x.first>y.second-y.first;
}
void solve(){
	int n,k;
	cin>>n>>k;
	for(int i=1;i<=k;i++){
		cin>>s[i].first>>s[i].second;
		for(int j=s[i].first+1;j<=s[i].second;j++){
			p[j]=j-1;
		}
	}
	sort(s+1,s+k+1,cmp);
	if(k==1){
		p[1]=0;
		for(int i=1;i<=n;i++){
			cout<<p[i]<<" ";
		}
		return;
	}
	if(s[k].second-s[k].first==s[1].second-s[1].first||(s[1].second-s[1].first==s[2].second-s[2].first&&s[1].second-s[1].first-s[k].second+s[k].first<=1)){
		cout<<"IMPOSSIBLE\n";
		return;
	}
	p[s[1].first]=0;
	p[s[k].first]=s[1].first+1;
	if(s[k].second-s[k].first==s[1].second-s[1].first-1){
		p[s[k].first]=s[1].first;
	}
	for(int i=2;i<k;i++){
		p[s[i].first]=s[1].first;
	}
	for(int i=1;i<=n;i++){
		cout<<p[i]<<" ";
	}
	cout<<"\n";
}
signed main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	int T=1;
	cin>>T;
	while(T--){
		solve();
	}
	return 0;
}