#include <bits/stdc++.h>
#define pii pair<int,int>
#define s1 first
#define s2 second
#define N 200011
using namespace std;
int T,n,k,fa[N];pii a[N];
bool cmp(pii a,pii b){return a.s2-a.s1+1>b.s2-b.s1+1;}
int main()
{
	scanf("%d",&T);while(T--)
	{
		scanf("%d%d",&n,&k);
		for(int i=1;i<=k;++i)scanf("%d%d",&a[i].s1,&a[i].s2);
		sort(a+1,a+1+k,cmp);
		if(k==1)
		{
			for(int i=0;i<n;++i)printf("%d ",i);putchar(10);
			continue;
		}
		if(a[1].s2-a[1].s1==a[k].s2-a[k].s1)
		{
			printf("IMPOSSIBLE\n");
			continue;
		}
		fa[a[1].s1]=0;
		for(int j=a[1].s1+1;j<=a[1].s2;++j)fa[j]=j-1;
		for(int i=2;i<=k;++i)
		{
			int len=a[i].s2-a[i].s1+1;
			int id=max(a[1].s1,a[1].s2-len);
			fa[a[i].s1]=id;
			for(int j=a[i].s1+1;j<=a[i].s2;++j)fa[j]=j-1;
		}
		for(int i=1;i<=n;++i)printf("%d ",fa[i]);putchar(10);
	}
	fclose(stdin);fclose(stdout);return 0;
}