1 #include<cstdio>
  2 #include<iostream>
  3 #include<vector>
  4 #include<cstring>
  5 #include<string>
  6 #include<stack>
  7 #include<algorithm>
  8 #include<map>
  9 using namespace std;
 10 
 11 struct Edge
 12 {
 13     int u,v;
 14 };
 15 
 16 const int N=10005;
 17 int dfn[N],low[N];
 18 int dfs_clock,m,n;
 19 map<string,int>ver;
 20 vector<int>G[N];
 21 vector<Edge>bridge;
 22 vector<Edge>edges;
 23 string guy[N];
 24 
 25 bool cmp(Edge a,Edge b)
 26 {
 27     if(a.u==b.u)
 28         return a.v<b.v;
 29     return a.u<b.u;
 30 }
 31 
 32 void init()
 33 {
 34     memset(low,0,sizeof(low));
 35     memset(dfn,0,sizeof(dfn));
 36     dfs_clock=0;
 37     edges.clear();
 38     bridge.clear();
 39     ver.clear();
 40     for(int i=0;i<n;i++)
 41         G[i].clear();
 42 }
 43 
 44 int tarjan(int u,int fa)
 45 {
 46     int lowu=dfn[u]=++dfs_clock;
 47     for(int i=0;i<G[u].size();i++)
 48     {
 49         int v=G[u][i];
 50         if(!dfn[v])
 51         {
 52             int lowv=tarjan(v,u);
 53             lowu=min(lowu,lowv);
 54         }
 55         else if(dfn[v]<dfn[u]&&v!=fa)
 56             lowu=min(dfn[v],lowu);
 57     }
 58     low[u]=lowu;
 59     return lowu;
 60 }
 61 
 62 int main()
 63 {
 64     int T;
 65     scanf("%d",&T);
 66     while(T--)
 67     {
 68         init();
 69         scanf("%d%d",&n,&m);
 70         int num=0;
 71         for(int i=0;i<m;i++)
 72         {
 73             string tmp1,tmp2;
 74             int u,v;
 75             cin>>tmp1>>tmp2;
 76             if(!ver.count(tmp1))
 77             {
 78                 ver[tmp1]=num;
 79                 guy[num]=tmp1;
 80                 num++;
 81             }
 82             if(!ver.count(tmp2))
 83             {
 84                 ver[tmp2]=num;
 85                 guy[num]=tmp2;
 86                 num++;
 87             }
 88             u=ver[tmp1],v=ver[tmp2];
 89             edges.push_back((Edge){u,v});
 90             G[u].push_back(v);
 91             G[v].push_back(u);
 92         }
 93         tarjan(0,-1);
 94         int j=0;
 95         for(j=0;j<n;j++)
 96             if(!dfn[j])break;
 97         if(j!=n)
 98             printf("0\n");
 99         else
100         {
101             vector<Edge>::iterator it;
102             for(it=edges.begin();it!=edges.end();it++)
103             {
104                 if(low[it->u]>dfn[it->v]||low[it->v]>dfn[it->u])
105                     bridge.push_back(*it);
106             }
107             printf("%d\n",bridge.size());
108             sort(bridge.begin(),bridge.end(),cmp);
109             vector<Edge>::iterator iter;
110             for(iter=bridge.begin();iter!=bridge.end();iter++)
111                 cout<<guy[iter->u]<<" "<<guy[iter->v]<<endl;
112         }
113     }
114     return 0;
115 }