#include <bits/stdc++.h>
#define int long long
#define lson k<<1
#define rson (k<<1)|1
#define debug cout<<666<<endl;
using namespace std;
const int N=1e6+5;
int fa[N];

void vision()
{
    int n,k;
    cin>>n>>k;
    for(int i=1;i<=n;i++){
        fa[i]=0;
    }
    vector<pair<int,int>>v;
    int ma=0,w=0;
    for(int i=1;i<=k;i++){
        int l,r;
        cin>>l>>r;
        for(int j=r;j>l;j--){
            fa[j]=j-1;
        }
        v.push_back({r-l+1,l});
        if(r-l+1>ma){
            ma=r-l+1;
            w=r;
        }
    }
    map<int,int>mp;
    int cnt=0;
    while(w!=0){
        mp[cnt]=w;
        w=fa[w];
        cnt++;
    }
    // cout<<mp[3]<<"\n";
    sort(v.begin(),v.end(),greater<>());
    if(v.size()==1){
        for(int i=1;i<=n;i++)cout<<fa[i]<<" ";
        cout<<"\n";
        return ;
    }
    else if(v.size()==2){
        if(v[0].first==v[1].first){
            cout<<"IMPOSSIBLE\n";
            return ;
        }
        else {
            fa[v[1].second]=mp[v[1].first];
        }
        for(int i=1;i<=n;i++)cout<<fa[i]<<" ";
        cout<<"\n";
        return ;
    }
    else {
        if(v[0].first==v[1].first){
            int ed=v.size();
            ed-=1;
            if(v[ed].first+1>=v[0].first){
                cout<<"IMPOSSIBLE\n";
                return ;
            }
        }
        for(int i=1;i<v.size();i++){
            fa[v[i].second]=mp[v[i].first];
        }
        for(int i=1;i<=n;i++)cout<<fa[i]<<" ";
        cout<<"\n";
        return ;
    }
    return ;
}
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int t=1;
    cin>>t;
    while(t--){
        vision();
    }
    return 0;
}