//Achen

 #include<algorithm>

 #include<iostream>

 #include<cstring>

 #include<cstdlib>

 #include<vector>

 #include<cstdio>

 #include<queue>

 #include<cmath>

 #include<set>

 #include<map>

 #define Formylove return 0

 #define For(i,a,b) for(int i=(a);i<=(b);i++)

 #define Rep(i,a,b) for(int i=(a);i>=(b);i--)

 const int N=;

 typedef long long LL;

 typedef double db;

 using namespace std;

 int n,m;

 template<typename T>void read(T &x)  {

     char ch=getchar(); x=; T f=;

     while(ch!='-'&&(ch<''||ch>'')) ch=getchar();

     if(ch=='-') f=-,ch=getchar();

     for(;ch>=''&&ch<='';ch=getchar()) x=x*+ch-''; x*=f;

 }

 struct edge {

     int u,v,cap,fl,nx;

     edge(){}

     edge(int u,int v,int cap,int fl,int nx):u(u),v(v),cap(cap),fl(fl),nx(nx){}

 }e[N];

 int ecnt=,fir[N];

 void add(int u,int v,int cap) {

     e[++ecnt]=edge(u,v,cap,,fir[u]); fir[u]=ecnt;

     //printf("%d->%d:%d\n",u,v,cap);

     e[++ecnt]=edge(v,u,,,fir[v]); fir[v]=ecnt;

 }

 queue<int>que;

 int d[N];

 void bfs(int s,int t) {

     que.push(t);

     For(i,,n) d[i]=n;

     d[t]=;

     while(!que.empty()) {

         int x=que.front();

         que.pop();

         for(int i=fir[x];i;i=e[i].nx) {

             int y=e[i].v;

             if(d[y]==n&&e[i].cap==) {

                 d[y]=d[x]+;

                 que.push(y);

             }

         }

     }

 }

 #define inf 1e9

 int p[N];

 int calc(int s,int t) {

     int fl=inf;

     for(int i=t;i!=s;i=e[p[i]].u)

         fl=min(fl,e[p[i]].cap-e[p[i]].fl);

     for(int i=t;i!=s;i=e[p[i]].u)

         e[p[i]].fl+=fl,e[p[i]^].fl-=fl;

     return fl;

 }

 int c[N],cur[N];

 int isap(int s,int t) {

     For(i,,n) c[i]=;

     bfs(s,t);

     For(i,,n) cur[i]=fir[i],c[d[i]]++;

     int rs=;

     for(int x=s;d[x]<n;) {

         if(x==t) {

             rs+=calc(s,t);

             x=s;

         }

         int ok=;

         for(int &i=cur[x];i;i=e[i].nx) if(e[i].cap>e[i].fl&&d[e[i].v]+==d[x]) {

             ok=; p[x=e[i].v]=i; break;

         }

         if(!ok) {

             int D=n; cur[x]=fir[x];

             for(int i=fir[x];i;i=e[i].nx) if(e[i].cap>e[i].fl)

                 D=min(D,d[e[i].v]+);

             if(!(--c[d[x]])) break;

             c[d[x]=D]++;

             if(x!=s) x=e[p[x]].u;

         }

     }

     return rs;

 }

 int dd[N];

 vector<int>vc;

 void init() {

     ecnt=;

     memset(fir,,sizeof(fir));

     memset(dd,,sizeof(dd));

 }

 int main() {

 #ifdef ANS

     freopen(".in","r",stdin);

     freopen(".out","w",stdout);

 #endif

     int T; read(T);

     while(T--) {

         init();

         read(n); read(m);

         For(i,,m) {

             int u,v,w;

             read(u); read(v); read(w);

             dd[u]++; dd[v]--;

             if(!w) add(u,v,);

         }

         int s=n+,t=n+,fl=; n+=;

         For(i,,n-) {

             if(dd[i]&) { fl=; break; }

             if(dd[i]>) add(s,i,dd[i]/);

             if(dd[i]<) add(i,t,(-dd[i])/);

             if(dd[i]!=) vc.push_back(ecnt-);

         }

         isap(s,t);

         int up=vc.size();

         For(i,,up-) if(e[vc[i]].fl!=e[vc[i]].cap) {

             fl=; break;

         } vc.clear();

         if(fl) puts("impossible");

         else puts("possible");

     }

     Formylove;

 }