#include <bits/stdc++.h>
using i64 = long long;
#define int i64
#define pb push_back
#define ep emplace
#define eb emplace_back
using std::cerr;
// using namespace std::views;
// using namespace std::ranges;
using std::max, std::min, std::swap, std::array;
using std::cin, std::cout, std::string, std::vector;
using std::ostream;
int read(int x = 0, int f = 0, char ch = getchar()) {
    while (ch < 48 or 57 < ch) f = ch == 45, ch = getchar();
    while(48 <= ch and ch <= 57) x = x * 10 + ch - 48, ch = getchar();
    return f ? -x : x;
}
template <class T1, class T2> ostream &operator<<(ostream &os, const std::pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << '\n'; }
using pii = std::pair<int, int>;
#define l first
#define r second

void solve() {
    int n = read();
    int k = read();
    vector<pii> a(k);
    for (auto &[l, r] : a) l = read(), r = read();
    std::ranges::sort(a, [&](pii a, pii b) {
        return a.r - a.l > b.r - b.l;
    });

    vector<int> ans(n + 1);
    vector<int> siz(n + 1);
    vector<int> son(n + 1);

    for (auto [l, r] : a) {
        for (int i = l + 1; i <= r; i++) {
            ans[i] = i - 1;
        }
    }

    auto [l, r] = a[0];
    son[r] = 0, siz[r] = 1;
    for (int i = k - 1; i; i--) {
        auto [x, y] = a[i];
        int len = y - x + 1;
        while (r > l and siz[son[r]] < len) {
            r--;
            son[r] = r + 1;
            siz[r] = siz[r + 1] + 1;
        }
        if (l == r and siz[son[r]] < len) {
            cout << "IMPOSSIBLE\n";
            return;
        }
        siz[r] += len;
        ans[x] = r;
    }

    for (int i = 1; i <= n; i++) {
        cout << ans[i] << " \n"[i == n];
    }
}

signed main() {
    for (int T = read(); T--; solve());
    // solve();
    return 0;
}