1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cmath>
 6 #include<queue>
 7 using namespace std;
 8 #define N 202
 9 #define M 5005
10 #define inf 0x3f3f3f3f
11 queue<int> q;
12 struct edge{
13     int to,next,c,f;
14 }e[M];
15 int pre[N],level[N],in[N];
16 int T,S,cnt;
17 void addedge(int u,int v,int c){
18     e[cnt].f=0,e[cnt].to=v,e[cnt].c=c,e[cnt].next=pre[u],pre[u]=cnt++;
19     e[cnt].f=0,e[cnt].to=u,e[cnt].c=0,e[cnt].next=pre[v],pre[v]=cnt++;
20 }
21 bool dinic_bfs(){
22     memset(level,0,sizeof(level));
23     q.push(S);
24     level[S]=1;
25     while(!q.empty()){
26         int u=q.front();q.pop();
27         for(int edg=pre[u];edg!=0;edg=e[edg].next){
28             int v=e[edg].to;
29             if(!level[v]&&e[edg].c>e[edg].f){
30                 level[v]=level[u]+1;
31                 q.push(v);
32             }
33         }
34     }
35     return level[T]!=0;
36 }
37 int dinic_dfs(int u,int cp){
38     int tmp=cp;
39     if(T==u)return cp;
40     for(int edg=pre[u];edg!=0&&tmp;edg=e[edg].next){
41         int v=e[edg].to;
42         if(level[v]==level[u]+1&&e[edg].c>e[edg].f){
43             int t=dinic_dfs(v,min(tmp,e[edg].c-e[edg].f));
44             e[edg].f+=t;
45             e[edg^1].f-=t;
46             tmp-=t;
47         }
48     }
49     return cp-tmp;
50 }
51 bool dinic(int s){
52     int tf=0,f=0;
53     while(dinic_bfs()){
54         while(f=dinic_dfs(S,inf)){
55             tf+=f;
56         }
57     }
58
59     return tf==s;
60 }
61 int main(){
62     int ca;
63     scanf("%d",&ca);
64     while(ca--){
65         int m,s,flag=1;
66         memset(pre,0,sizeof(pre));
67         memset(in,0,sizeof(in));
68         scanf("%d%d",&m,&s);S=0;
69         T=m+1;cnt=2;
70         while(s--){
71             int u,v,c;
72             scanf("%d%d%d",&u,&v,&c);
73             in[u]--;in[v]++;
74             if(!c)addedge(u,v,1);
75         }
76         for(int i=1;i<=m;i++)
77         {
78             if(in[i]&1)flag=0;
79         }
80         int sum=0;
81         if(flag){
82             for(int i=1;i<=m;i++){
83                 if(in[i]>0){addedge(i,T,in[i]>>1);sum+=in[i]>>1;}
84                 if(in[i]<0)addedge(S,i,(-in[i])>>1);
85             }
86         }
87         if(!dinic(sum))flag=0;
88         if(!flag)printf("impossible\n");
89         else printf("possible\n");
90     }
91     return 0;
92 }