#include<bits/stdc++.h>
using namespace std;
// #define int long long
#define debug(x) cout<<x<<"--------------------------------------\n" ;
const int N = 1e5 + 10;
typedef long long ll;
const int INF = 1e9;
const int MOD = 1e9 + 7;
typedef pair<int, int> PII;

int gcd(int a, int b) {
    return b ? gcd(b, a % b) : a;
}

ll qpow(int a, int k) {
    ll res = 1;
    while (k) {
        if (k & 1) res = 1ll * res * a % MOD;
        a = 1ll * a * a % MOD;
        k >>= 1;
    }
    return res;
}

int n, m, k;
string s;

void solve() {
    cin >> n >> k;
    vector<PII> seg(k+1);
    for(int i=1;i<=k;i++) {
        cin >> seg[i].first >> seg[i].second;
    }
    sort(seg.begin()+1,seg.end(),[&](PII a,PII b) {
        return (a.second - a.first) > (b.second - b.first);
    });
    int mx = seg[1].second-seg[1].first;
    vector<vector<int>> pos(mx+1);
    vector<int> fa(n+1);
    // debug(1)
    // cout << mx << '\n';
    // cout << seg[1].first << ' ' << seg[1].second << '\n';
    for(int i=1;i<=k;i++) {
        // debug(i)
        int len = seg[i].second-seg[i].first+1;
        if(i==1) {
            fa[seg[1].first] = 0;
        } else {

            if(len>mx || pos[len].empty()) {
                cout << "IMPOSSIBLE\n";
                return;
            }
            fa[seg[i].first] = pos[len][0];
        }
        for(int x=seg[i].first;x<=seg[i].second-1;x++) {
            pos[seg[i].second-x].push_back(x);
        }
        for(int j=seg[i].first+1;j<=seg[i].second;j++) {
            fa[j] = j-1;
        }
    }
    for(int i=1;i<=n;i++) {
        cout << fa[i] << " \n"[i==n];
    }
}

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