#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define db double
#define pii pair<int,int>
#define fi first
#define se second
//cout<<setiosflags(ios::fixed)<<setprecision(K);
const int dx[4]={1,-1,0,0};
const int dy[4]={0,0,1,-1};
const double eps=1e-9; 
const double PI=acos(-1.0);
const int inf=1e9+7;
const int mod=998244353;
const int N=2e5+10,M=N<<1;

void solve(){
    int n,m;
    cin>>n>>m;
    vector<pii>a(m);
    for(int i=0;i<m;i++){
        int l,r;
        cin>>l>>r;
        a[i]={r-l+1,l};
    }
    sort(a.begin(),a.end(),greater<pii>());

    if(m==1){
        for(int i=0;i<n;i++){
            cout<<i<<' ';
        }
        cout<<'\n';
        return;
    }

    if(a[0].fi==a[m-1].fi){
        cout<<"IMPOSSIBLE\n";
        return;
    }
    if(a[0].fi==2&&a[0].fi==a[1].fi&&a[m-1].fi==1){
        cout<<"IMPOSSIBLE\n";
        return;
    }

    vector<int>p(n+1);
    auto [sz,L]=a[0];
    int R=L+sz-1;
    p[L]=0;
    for(int i=L+1;i<=R;i++){
        p[i]=i-1;
    }

    int rt=L;
    
    if(a[0].fi==a[1].fi){
        auto [sz2,L2]=a[m-1];
        int R2=L2+sz2-1;

        for(int i=L2+1;i<=R2;i++){
            p[i]=i-1;
        }
        p[L2]=rt+1;
        m--;
    }
    
    
    for(int i=1;i<m;i++){
        auto [sz,l]=a[i];
        int r=l+sz-1;
        for(int i=l+1;i<=r;i++){
            p[i]=i-1;
        }
        p[l]=rt;
    }
    for(int i=1;i<=n;i++){
        cout<<p[i]<<' ';
    }
    cout<<'\n';
}

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