#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <queue>
#include <map>
#include <set>
using namespace std;
using ll=long long;
const int maxn=2e5+5;
const ll mod=998244353;
int fa[maxn];
struct node{
    int l,r,len;
    bool operator < (const node &nd) const {
        return len>nd.len;
    }
} p[maxn];
void solve() {
    int n,k;
    cin>>n>>k;
    for(int i=0;i<k;i++) {
        cin>>p[i].l>>p[i].r;
        p[i].len=p[i].r-p[i].l+1;
    }
    sort(p,p+k);
    int rt=p[0].l;
    if(p[0].len==1&&k!=1) {
        cout<<"IMPOSSIBLE\n";
        return;
    }
    for(int i=0;i<k;i++) {
        int last=rt;
        for(int j=p[i].l;j<=p[i].r;j++) {
            fa[j]=last;
            last=j;
        }
    }
    fa[rt]=0;
    for(int i=1;i<=n;i++) {
        cout<<fa[i]<<" ";
    }
    cout<<"\n";
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t;
    cin>>t;
    while (t--) {
        solve();
    }
    return 0;
}