#include<bits/stdc++.h>
#define int long long
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define pb push_back
#define pii pair<int,int>
using namespace std;
//const int mod=998244353;
int gcd(int a,int b){return b?gcd(b,a%b):a;};
int qpw(int a,int b,int mod){int ans=1;while(b){if(b&1)ans=ans*a%mod;a=a*a%mod,b>>=1;}return ans;}
//int inv(int x){return qpw(x,mod-2);}
const int N=2e5+10;
bool cmp(pii a,pii b){
    return a.second-a.first>b.second-b.first;
}
void solve(){
    int len,n;cin>>len>>n;
    vector<pii>a(n);
    vector<int>fa(len+1);
    for(int i=0;i<n;i++)cin>>a[i].first>>a[i].second;
    sort(all(a),cmp);
    int mx_len=a[0].second-a[0].first;
    int mi_len;
    bool ok=true;
    bool flag=false;
    for(int i=1;i<n;i++){
        int now_len=a[i].second-a[i].first;
        if(now_len==mx_len)flag=true;
        mi_len=now_len;
    }
    if(flag&&mx_len-mi_len<=1){
        cout<<"IMPOSSIBLE\n";
        return;
    }
    int mx_fa=-1;
    int second_fa;
    for(int i=a[0].first;i<=a[0].second;i++){
        if(mx_fa==-1){
            fa[i]=0;
            mx_fa=i;
        }else if(i-1==a[0].first){
            second_fa=i;
            fa[i]=i-1;
        }else fa[i]=i-1;
    }
    if(mx_len-mi_len==1)
    {
        for(int i=1;i<n;i++){
            int now_len=a[i].second-a[i].first;
            fa[a[i].first]=mx_fa;
            for(int j=a[i].first+1;j<=a[i].second;j++){
                fa[j]=j-1;
            }
        }
    }
    else for(int i=1;i<n;i++){
        int now_len=a[i].second-a[i].first;
        if(now_len==mx_len)fa[a[i].first]=mx_fa;
        else fa[a[i].first]=second_fa;
        for(int j=a[i].first+1;j<=a[i].second;j++){
            fa[j]=j-1;
        }
    }

    for(int i=1;i<=len;i++){
        cout<<fa[i]<<" \n"[i==len];
    }
}
signed main(){
    ios::sync_with_stdio(false),cin.tie(nullptr),cout.tie(nullptr);
    int _=1;
    cin>>_;
    while(_--)solve();
}