#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using uint = unsigned int;
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define eb emplace_back
#define F first
#define S second
#define put(x) cout << (x) << '\n'

const int N = 2e5 + 5;
const int MOD = 998244353;

template <typename T, typename U>
ostream& operator<<(ostream& os, pair<T, U> p) {
    return os << "(" << p.first << ", " << p.second << ")";
}
template<typename T, typename U = char>
void print(const T &v, U end = ' ') {
    for (auto it : v) cout << it << end;
    cout << '\n';
}




void solve() {
    int n, k;
    cin >> n >> k;

    vector<pair<int, int>> chains(k);
    int mx = 0, mn = 1e9, cnt = 0;
    for(auto &[l, r] : chains){
        cin >> l >> r;
        int length = r - l + 1;
        mn = min(mn, length);
        if(length > mx) mx = length, cnt = 0;
        else if(length == mx) cnt++;
    }

    if(n == 1){
        for(int i = 0; i < n; i++) cout << i << ' ';
        cout << '\n';
        return;
    }
    if(mx == mn || (mx == mn + 1 && cnt > 1)){
        put("IMPOSSIBLE");
        return;
    }


    vector<int> ans(n + 1, 0);
    sort(all(chains), [&](pair<int, int> ch1, pair<int, int> ch2){
         return ch1.S - ch1.F > ch2.S - ch2.F;
         });

    auto [l1, r1] = chains[0];
    auto [l2, r2] = chains[k - 1];
    ans[l2] = r1 - (r2 - l2 + 1);
    for(int i = 1; i < k - 1; i++) ans[chains[i].F] = l1;
    for(auto [l, r] : chains){
        for(int i = l + 1; i <= r; i++) ans[i] = i - 1;
    }

    ans.erase(ans.begin());
    print(ans);



}

int32_t main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int test_cases;
    cin >> test_cases;
    while (test_cases--) {
        solve();
    }
    return 0;
}