#include<bits/stdc++.h>
using namespace std;
int read(){
	int num=0;bool flag=1;
	char c=getchar();
	for(;c<'0'||c>'9';c=getchar())
		if(c=='-')flag=0;
	for(;c>='0'&&c<='9';c=getchar())
		num=(num<<1)+(num<<3)+c-'0';
	return flag?num:-num;
}
const int N=1e5+10;
int n,k,ans[N];
array<int,2>a[N];
bool cmp(array<int,2>A,array<int,2>B){
	return (A[1]-A[0])>(B[1]-B[0]);
}
signed main(){
	int T=read();
	while(T--){
		n=read();k=read();
		for(int i=1;i<=k;i++){
			a[i][0]=read();
			a[i][1]=read();
			for(int j=a[i][0];j<a[i][1];j++){
				ans[j+1]=j;
			}
		}
		if(n==1){
			printf("0\n");
			continue;
		}
		if(n==2&&k==1){
			printf("0 1\n");
			continue;
		}
		sort(a+1,a+k+1,cmp);
		if(n>2&&(a[1][1]-a[1][0]+1==1||a[1][1]-a[1][0]+1==2&&a[2][1]-a[2][0]+1==2)){
			printf("IMPOSSIBLE\n");
			continue;
		}
		if((a[1][1]-a[1][0]+1)-(a[k][1]-a[k][0]+1)<=1&&(a[2][1]-a[2][0]+1)==(a[1][1]-a[1][0]+1)){
			printf("IMPOSSIBLE\n");
			continue;
		}
		ans[a[1][0]]=0;
		for(int i=2;i<=k;i++){
			if(a[i][1]-a[i][0]+1>=a[1][1]-a[1][0]){
				ans[a[i][0]]=a[1][0];
			}
			else{
				ans[a[i][0]]=a[1][0]+1;
			}
		}
		for(int i=1;i<=n;i++){
			printf("%d ",ans[i]);
		}
		printf("\n");
	} 
	return 0;
}