#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define endl "\n"
#define double long double

const int N = 3e5 + 10;
const ll INF = 0x3f3f3f3f3f3f3f;

ll n, m, k;
bool cmp(pll a,pll b){
  return a.first>b.first;
}
void solve()
{
  cin>>n>>k;
  vector<ll>ans(n+5,0);
  vector<pll>len(k+5);
  for(int i=1;i<=k;i++){
    ll l,r;cin>>l>>r;
    ans[l]=-1;
    for(int j=l+1;j<=r;j++){
      ans[j]=j-1;
    }
    len[i]={r-l+1,l};
  }
  sort(len.begin()+1,len.begin()+1+k,cmp);
  ans[len[1].second]=0;
  if(len[2].first==len[1].first){
    if(len[k].first<=len[1].first-2){
      ans[len[k].second]=len[1].first+1;
    }
    else{
      cout<<"IMPOSSIBLE\n";return;
    }
  }
  for(int i=1;i<=n;i++){
    if(ans[i]==-1){
      cout<<len[1].second<<' ';
    }
    else cout<<ans[i]<<' ';
  }
  cout<<endl;
}
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  int _ = 1;
  cin >> _;
  while (_--)
    solve();
  return 0;
}