#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<LL,LL> PII;
const int N=5e5+10,M=2*N;
//const int mod=998244353;
const LL mod=1e9+7;
const LL INF=1e18+7;
//LL h[N],e[M],ne[M],idx;


void solve(){
    int n,k;
    cin>>n>>k;


    vector<PII> a(k);
    vector<int> res(n+1);

    for(int i=0;i<k;i++){
        int l,r;
        cin>>l>>r;

        for(int j=l+1;j<=r;j++) res[j]=j-1;

        a[i]={r-l+1,l};
    }


    sort(a.begin(),a.end());


    if(a[k-1].first==1){
        cout<<"IMPOSSIBLE"<<endl;
        return;
    }


    for(int i=0;i<k-1;i++) res[a[i].second]=a[k-1].second;


    for(int i=1;i<=n;i++) cout<<res[i]<<" ";

    cout<<endl;


}
 
 
 int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T=1;
    cin>>T;
    
    while(T--) solve();
 
    return 0;
}