#include<random>
#include<iostream>
#include<iomanip>
#include<ctime>
#include<cmath>
#include<cctype>
#include<cstdio>
#include<cstdlib>
#include<climits>
// #define NDEBUG
#include<cassert>
#include<cstring>
#include<complex>
#include<algorithm>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<vector>
#include<bitset>
// #define LL __int128
#define LL long long
#define ULL unsigned LL
#define uint unsigned int
// #define int LL
// #define double long double
#define mkp make_pair
#define par pair<int,int>
#define epb emplace_back
#define psb push_back
#define f(x) ((x).first)
#define s(x) ((x).second)
using namespace std;
#define Lbt(x) ((x)&(-(x)))
#define Swap(x,y) (x^=y^=x^=y)
const int Mxxx=1e5;
inline char gc()
{
    // return getchar();
    static char buf[Mxxx],*p1=buf,*p2=buf;
    return (p1==p2&&(p2=(p1=buf)+fread(buf,1,Mxxx,stdin),p1==p2))?EOF:*p1++;
}
inline char pc(char ch,bool fl=false)
{
    // return fl?0:putchar(ch),0;
    static char buf[Mxxx],*p1=buf,*p2=buf+Mxxx;
    return (fl||((*p1++=ch)&&p1==p2))&&(fwrite(buf,1,p1-buf,stdout),p1=buf),0;
}
#define output pc('!',true)
inline int read()
{
    char ch=gc();
    int gans=0,gflag=0;
    for(;ch<'0'||'9'<ch;ch=gc())gflag|=(ch=='-');
    for(;'0'<=ch&&ch<='9';ch=gc())gans=(gans<<1)+(gans<<3)+(ch^48);
    return gflag?-gans:gans;
}
template<typename T>
inline char read(T&gans)
{
    char ch=gc();
    int gflag=0;gans=0;
    for(;ch<'0'||'9'<ch;ch=gc())gflag|=(ch=='-');
    for(;'0'<=ch&&ch<='9';ch=gc())gans=(gans<<1)+(gans<<3)+(ch^48);
    return gans=gflag?-gans:gans,ch;
}
template<typename T>
inline void write(T x)
{
    if(x>9)write(x/10);
    pc(x%10^48);
}
template<typename T>
inline void writenum(T x,char ch)
{
    if(x<0)pc('-'),x=-x;
    write(x),pc(ch);
}
inline void writechar(char x,char ch)
{
    pc(x),pc(ch);
}
template<typename T>
inline T Max(T x,T y)
{
    return x>y?x:y;
}
template<typename T>
inline T Min(T x,T y)
{
    return x<y?x:y;
}
template<typename T>
inline T Abs(T x)
{
    return x<0?-x:x;
}
template<typename T>
inline void ckmx(T&x,T y)
{
    x=Max(x,y);
}
template<typename T>
inline void ckmn(T&x,T y)
{
    x=Min(x,y);
}
int TT;
const int Mx=2e5;
int n,K,psl[Mx+5],psr[Mx+5];
int tt[Mx+5],ans[Mx+5];
signed main()
{
    #ifndef ONLINE_JUDGE
    freopen("_.in","r",stdin);
    // freopen("_.out","w",stdout);
    #endif
    int i,j,k,l,f,mx,rt,lf;
    for(TT=read();TT;TT--)
    {
        n=read();K=read();
        for(i=1;i<=n;i++)tt[i]=0;
        for(i=1;i<=K;i++)psl[i]=read(),psr[i]=read();
        for(i=1;i<=K;i++)tt[psr[i]-psl[i]+1]++;
        for(i=1;i<=n;i++)if(tt[i])mx=i;
        f=0;for(i=1;i<mx-1;i++)f|=tt[i];
        if(tt[mx]^1&&!f)output,puts("IMPOSSIBLE");
        else
        {
            for(i=1;i<=K;i++)if(psr[i]-psl[i]+1==mx)break;
            assert(i<=K);rt=psl[i];lf=psr[i];
            for(j=psr[i];j>psl[i];j--)ans[j]=j-1;
            ans[j]=0;
            for(j=1;j<=K;j++)if(i^j)
            {
                l=psr[j]-psl[j]+1;
                for(k=psr[j];k>psl[j];k--)ans[k]=k-1;
                ans[k]=lf-Min(l,mx-1);
            }
            for(i=1;i<=n;i++)writenum(ans[i],i==n?10:32);
        }
    }
    return output;
}
/*
1 9 4
1 3
4 6
7 8
9 9
*/
/*
1 8 3
1 3
4 6
7 8
*/
/*
 3
 12 5
 1 5
 9 11
 7 8
 6 6
 12 12
 4 3
 1 1
 4 4
 2 3
 2 2
 1 1
 2 2
*/