#include<bits/stdc++.h>
using namespace std;
const long double PI = acos(-1);
//#define int long long
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef pair<ll, ll> PLL;
typedef tuple<ll, ll, ll> TLL;
int lowbit(int x) {return x & (- x);};
const int N = 200010, mod = 998244353;
const int Mod = 1e9 + 7, INF = 0x3f3f3f3f;

void solve(){
    ll n, k;
    cin >> n >> k;
    vector<PLL> seg(k + 1);
    vector<PLL> l1, l2, l3;
    ll maxlen = 0;
    for(int i = 1; i <= k; i ++){
        ll l, r;
        cin >> l >> r;
        seg[i] = {l, r};
        ll len = r - l;
        maxlen = max(maxlen, len);
    }
    if(n == 1){
        for(int i = 1; i <= n; i ++) cout << i - 1 << ' ';
        cout << '\n';
        return;
    }
    bool ok = 1;
    ll pl = 0, pr = 0;
    for(int i = 1; i <= k; i ++){
        auto [l, r] = seg[i];
        ll len = r - l;
        if(len == maxlen){
            if(ok == 1){
                pl = l, pr = r;
                ok ^= 1;
            }
            else l2.push_back({l, r});
        }
        else if(len == maxlen - 1){
            l3.push_back({l, r});
        }
        else l1.push_back({l, r});
    }
    ll p = 0;
    if(l2.size()) p = max(p, maxlen);
    if(l3.size()) p = max(p, maxlen - 1);
    vector<ll> ans(n + 1);
    ans[pl] = 0;
    for(int i = pl + 1; i <= pr; i ++) ans[i] = i - 1;
    ll siz = maxlen;
    for(auto [l, r] : l1){
        ll len = r - l;
        siz += len + 1;
        ll rt = pr - len - 1;
        //cout << l << ' ' << r << ' ' << rt << '\n';
        ans[l] = rt; 
        for(int i = l + 1; i <= r; i ++) ans[i] = i - 1;
    }
    ll ss = 0;
    for(int i = 1; i <= n; i ++){
        auto [l, r] = seg[i];
        ss += (r - l == maxlen);
    }
  
    if(siz < p || ss == n){
        cout << "IMPOSSIBLE\n";
    }
    else{
        for(auto [l, r] : l2){
            ans[l] = pl;
            for(int i = l + 1; i <= r; i ++) ans[i] = i - 1;
        }
        for(auto [l, r] : l3){
            ans[l] = pl;
            for(int i = l + 1; i <= r; i ++) ans[i] = i - 1;
        }        
        for(int i = 1; i <= n; i ++){
            cout << ans[i] << " \n"[i == n];
        }
    }
}

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