#include<bits/stdc++.h>
#define ll long long
using namespace std;
int T;
int N,K;
struct node
{
    int L,R;
}Interval[100001];
int Fa[100001];
bool Cmp(node A,node B)
{
    return A.R-A.L<B.R-B.L;
}
void Solve()
{
    scanf("%d%d",&N,&K);
    for(int i=1;i<=K;++i)
    scanf("%d%d",&Interval[i].L,&Interval[i].R);
    sort(Interval+1,Interval+K+1,Cmp);
    int Root=Interval[K].L;
    int Sz=Interval[K].R-Interval[K].L;
    int Ch=Sz;
    for(int i=1;i<=K;++i)
    {
        Fa[Interval[i].L]=(i==K?0:Root);
        if(Interval[i].R-Interval[i].L+1<=Ch-1)
        {
            Fa[Interval[i].L]=Root+1;
            Sz+=Interval[i].R-Interval[i].L+1;
        }
        for(int j=Interval[i].L+1;j<=Interval[i].R;++j)
        Fa[j]=j-1;
    }
    if(Sz<Interval[K-1].R-Interval[K-1].L+1)
    {
        puts("IMPOSSIBLE");
        return;
    }
    for(int i=1;i<=N;++i)
    printf("%d ",Fa[i]);
    putchar('\n');
}
int main()
{
    scanf("%d",&T);
    while(T--)
    {
        Solve();
    }
}