#include<stdio.h>
#include<iostream>
#include<algorithm>
#define inf 0X7fffffff
using namespace std;
const int N=5e5+9;
int read(int &x){
    int dat=0,oko=1;char chc=getchar();
    while(chc<'0'||chc>'9'){if(chc=='-')oko=-1;chc=getchar();}
    while(chc>='0'&&chc<='9'){dat=dat*10+chc-'0';chc=getchar();}
    x=dat*oko;return x;
}int n,m,ans[N],root;
struct node{
    int l,r,len;
}a[N];bool cmp(node A,node B){
    return A.len>B.len;
}
void solve(){
    cin>>n>>m;
    for(int i=1;i<=n;i++)ans[i]=0;
    for(int i=1;i<=m;i++){
        cin>>a[i].l>>a[i].r;
        a[i].len=a[i].r-a[i].l+1;
    }sort(a+1,a+1+m,cmp);
    if(m>1&&a[1].len==a[2].len){
        cout<<"IMPOSSIBLE"<<"\n";
        return;
    }root=a[1].l;
    for(int i=2;i<=m;i++){
        ans[a[i].l]=root;
    }for(int i=1;i<=n;i++){
        if(root==i||ans[i]){
            cout<<ans[i]<<" ";
        }else cout<<i-1<<" ";
    }cout<<"\n";
}
int main(){
    int T;cin>>T;
    while(T--)solve();
    return 0;
}