#include<bits/stdc++.h>
#define ull unsigned long long
#define ll long long
#define db double
#define file(a) freopen(#a".in", "r", stdin), freopen(#a".out", "w", stdout)
#define sky fflush(stdout)
#define gc getchar
#define pc putchar
namespace IO{
	template<class T>
	inline void read(T &s){
		s = 0;char ch = gc();bool f = 0;
		while(ch < '0' || '9'<ch) {if(ch == '-') f = 1; ch = gc();}
		while('0'<=ch && ch<='9') {s = s * 10 + (ch ^ 48); ch = gc();}
		if(ch == '.'){
			T p = 0.1;ch = gc();
			while('0' <= ch && ch <= '9') {s = s + p * (ch ^ 48);p /= 10;ch = gc();}
		}
		s = f ? -s : s;
	}
	template<class T,class ...A>
	inline void read(T &s,A &...a){
		read(s); read(a...);
	}
	template<class T>
	inline void print(T x){
		if(x<0) {x = -x; pc('-');}
		static char st[40];
		static int top;
		top = 0;
		do{st[++top] = x - x / 10 * 10 + '0';} while(x /= 10);
		while(top) {pc(st[top--]);}
	}
	template<class T,class ...A>
	inline void print(T s,A ...a){
		print(s); print(a...);
	}
};
using IO::read;
using IO::print;
const int N = 1e5;
int n, m;
struct node{
	int l, r;
}p[N + 3];
int fa[N + 3];
inline void solve(){
	read(n, m);
	for(int i = 1; i <= n; ++i) fa[i] = 0;
	for(int i = 1; i <= m; ++i){
		read(p[i].l, p[i].r);
		for(int j = p[i].l + 1; j <= p[i].r; ++j){
			fa[j] = j - 1;
		}
	}
	std::sort(p + 1, p + 1 + m, [](const node &x, const node &y){
		return x.r - x.l + 1 > y.r - y.l + 1;
	});
	int mxlen = p[1].r - p[1].l + 1, mxcnt = 0;
	for(int i = 1; i <= m; ++i){
		if(mxlen == p[i].r - p[i].l + 1){
			++mxcnt;
		}
	}
	if(mxcnt > 1){
		if(n - mxcnt){
			for(int i = 2; i < m; ++i){
				fa[p[i].l] = p[1].l;
			}
			fa[p[m].l] = p[1].l + 1;
		}else{
			printf("IMPOSSIBLE\n");
			return;
		}
	}else{
		for(int i = 2; i <= m; ++i){
			fa[p[i].l] = p[1].l;
		}
	}
	for(int i = 1; i <= n; ++i){
		printf("%d%c", fa[i], (i == n)[" \n"]);
	}
}
int main(){
#ifdef LOCAL
	file(a);
#endif
	int T; read(T);
	while(T--){
		solve();
	}
	return 0;
}