// what is matter? never mind. 
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2")
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
//#define ull unsigned long long
#define SZ(x) ((int)((x).size()))
#define ALL(x) (x).begin(),(x).end()
using namespace std;
inline int read()
{
	char c=getchar();int x=0;bool f=0;
	for(;!isdigit(c);c=getchar())f^=!(c^45);
	for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
	return f?-x:x;
}

#define mod 998244353
struct modint{
	unsigned int x;
	modint(int o=0){x=o;}
	modint &operator = (int o){return x=o,*this;}
	modint &operator +=(modint o){return x=x+o.x>=mod?x+o.x-mod:x+o.x,*this;}
	modint &operator -=(modint o){return x=x<o.x?x-o.x+mod:x-o.x,*this;}
	modint &operator *=(modint o){return x=1ll*x*o.x%mod,*this;}
	modint &operator ^=(int b){
		modint a=*this,c=1;
		for(;b;b>>=1,a*=a)if(b&1)c*=a;
		return x=c.x,*this;
	}
	modint &operator /=(modint o){return *this *=o^=mod-2;}
	friend modint operator +(modint a,modint b){return a+=b;}
	friend modint operator -(modint a,modint b){return a-=b;}
	friend modint operator *(modint a,modint b){return a*=b;}
	friend modint operator /(modint a,modint b){return a/=b;}
	friend modint operator ^(modint a,int b){return a^=b;}
	friend bool operator ==(modint a,modint b){return a.x==b.x;}
	friend bool operator !=(modint a,modint b){return a.x!=b.x;}
	bool operator ! () {return !x;}
	modint operator - () {return x?mod-x:0;}
	bool operator <(const modint&b)const{return x<b.x;}
};
inline modint qpow(modint x,int y){return x^y;}

vector<modint> fac,ifac,iv;
inline void initC(int n)
{
	if(iv.empty())fac=ifac=iv=vector<modint>(2,1);
	int m=iv.size(); ++n;
	if(m>=n)return;
	iv.resize(n),fac.resize(n),ifac.resize(n);
	For(i,2,n-1)fac[i]=fac[i-1]*i;
	ifac[n-1]=1/fac[n-1];
	Rep(i,n-2,0)ifac[i]=ifac[i+1]*(i+1),iv[i+1]=ifac[i+1]*fac[i];
}
inline modint C(int n,int m){
	if(m<0||n<m)return 0;
	return initC(n),fac[n]*ifac[m]*ifac[n-m];
}
inline modint sign(int n){return (n&1)?(mod-1):(1);}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 1000005
#define inf 0x3f3f3f3f

int n,m;
pii a[maxn];
int fa[maxn];

void work()
{
	n=read(),m=read();
	For(i,1,n)fa[i]=0;
	For(i,1,m){
		a[i].fi=read(),a[i].se=read();
		For(j,a[i].fi+1,a[i].se) fa[j]=j-1;
	}
	sort(a+1,a+m+1,[&](pii x,pii y){
		return x.se-x.fi > y.se-y.fi;
	});
	if(m==1 || a[1].se-a[1].fi > a[2].se-a[2].fi) {
		For(i,2,m) fa[a[i].fi]=a[1].fi;
	}else{
		if(a[m].se-a[m].fi >= a[1].se-a[1].fi-1) {
			puts("IMPOSSIBLE");
			return;
		}else{
			For(i,2,m) {
				if(a[i].se-a[i].fi == a[1].se-a[1].fi) {
					fa[a[i].fi]=a[1].fi;
				}else{
					fa[a[i].fi]=a[1].fi+1;
				}
			}
		}
	}
	For(i,1,n)cout<<fa[i]<<" "; cout<<endl;
}

signed main()
{
	int T=read();
	while(T--)work();
	return 0;
}
/*

*/