#include<cstdio>
#include<algorithm>
const int N = 1e5 + 10;
int n, m, fa[N];
std::pair<int, int> chain[N];
int main() {
    int t; scanf("%d", &t);
    while(t--) {
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= m; i++) {
            int l, r; scanf("%d%d", &l, &r);
            chain[i] = {r - l + 1, l};
            for(int i = l + 1; i <= r; i++) {
                fa[i] = i - 1;
            }
        }
        std::sort(chain + 1, chain + 1 + m);
        std::reverse(chain + 1, chain + 1 + m);
        if(m >= 2 && chain[1].first == chain[2].first) {
            puts("IMPOSSIBLE");
            continue;
        }
        int dep = chain[1].first - 1, now = chain[1].second; 
        fa[now] = 0;
        for(int i = 2; i <= m; i++) {
            while(dep > chain[i].first) --dep, ++now;
            fa[chain[i].second] = now;
        }
        for(int i = 1; i <= n; i++) {
            printf("%d%c", fa[i], " \n"[i == n]);
        }
    }
    return 0;
}