#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
int const xn=205,xm=3005,inf=0x3f3f3f3f;
int n,m,hd[xn],ct=1,to[xm],nxt[xm],dis[xn],cur[xn],c[xm],ind[xn],cd[xn];
queue<int>q;
int rd()
{int ret=0,f=1; char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=0; ch=getchar();}while(ch>='0'&&ch<='9')ret=ret*10+ch-'0',ch=getchar();return f?ret:-ret;
}
void add(int x,int y,int z){to[++ct]=y; nxt[ct]=hd[x]; hd[x]=ct; c[ct]=z;}
int abss(int x){return x>0?x:-x;}
bool bfs()
{while(q.size())q.pop();memset(dis,0,sizeof dis);dis[0]=1; q.push(0);while(q.size()){int x=q.front(); q.pop();for(int i=hd[x],u;i;i=nxt[i])if(!dis[u=to[i]]&&c[i])dis[u]=dis[x]+1,q.push(u);}return dis[n+1];
}
int dfs(int x,int fl)
{if(x==n+1)return fl;int ret=0;for(int &i=cur[x],u;i;i=nxt[i]){if(dis[u=to[i]]!=dis[x]+1||!c[i])continue;int tmp=dfs(u,min(fl-ret,c[i]));if(!tmp)dis[u]=0;c[i]-=tmp; c[i^1]+=tmp;ret+=tmp; if(ret==fl)break;}return ret;
}
int main()
{int T=rd();while(T--){ct=1; memset(hd,0,sizeof hd);memset(ind,0,sizeof ind); memset(cd,0,sizeof cd);n=rd(); m=rd();for(int i=1,x,y,z;i<=m;i++){x=rd(); y=rd(); z=rd();cd[x]++; ind[y]++;if(!z)add(y,x,1),add(x,y,0);}bool fl=0; int goal=0;for(int i=1;i<=n;i++){if(abss(ind[i]-cd[i])%2){fl=1; break;}if(ind[i]>cd[i])add(0,i,(ind[i]-cd[i])/2),add(i,0,0),goal+=(ind[i]-cd[i])/2;else if(ind[i]<cd[i])add(i,n+1,(cd[i]-ind[i])/2),add(n+1,i,0);}if(fl){puts("impossible"); continue;}int ans=0;while(bfs()){memcpy(cur,hd,sizeof hd);ans+=dfs(0,inf);}if(ans==goal)puts("possible");else puts("impossible");}return 0;
}