1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<vector>
 6 #include<map>
 7 #include<string>
 8 using namespace std;
 9 const int maxn=100007;
10 struct node
11 {
12     int from,to;
13 };
14 node edge[100007*2];
15 int next1[100007*2],first[maxn],pre[maxn],top;
16 int n,m,sum,ans[maxn],anstop;
17 void addedge(int u,int v)
18 {
19     edge[sum].from=u;edge[sum].to=v;
20     next1[sum]=first[u];first[u]=sum;sum++;
21     edge[sum].from=v;edge[sum].to=u;
22     next1[sum]=first[v];first[v]=sum;sum++;
23 }
24 int tarjain(int u,int fa)
25 {
26     int lowu=pre[u]=top++,child=0;
27     for(int i=first[u];i!=-1;i=next1[i])
28     {
29         int v=edge[i].to;
30         if(!pre[v]){
31             child++;
32             int lowv=tarjain(v,u);
33             lowu=min(lowv,lowu);
34             if(pre[u]<lowv){
35                 ans[anstop++]=i;
36             }
37         }
38         else if(pre[v]<lowu&&v!=fa){
39             lowu=min(lowu,pre[v]);
40         }
41     }
42     return lowu;
43 }
44 int main()
45 {
46     ios::sync_with_stdio(false);
47     int t;string s1,s2;int cnt;
48     cin>>t;
49     while(t--){
50         memset(next1,-1,sizeof(next1));
51         memset(first,-1,sizeof(first));
52         memset(pre,0,sizeof(pre));
53         map<string,int> mp1;
54         map<int,string> mp2;
55         cin>>n>>m;
56         cnt=1;anstop=0,sum=0;
57         for(int i=1;i<=m;i++)
58         {
59             cin>>s1>>s2;
60             if(mp1[s1]==0) mp1[s1]=cnt,mp2[cnt]=s1,cnt++;
61             if(mp1[s2]==0) mp1[s2]=cnt,mp2[cnt]=s2,cnt++;
62             addedge(mp1[s1],mp1[s2]);
63         }
64         top=1;
65         tarjain(1,-1);
66         bool flag=1;
67         for(int i=1;i<=n;i++)
68         {
69             if(!pre[i]) flag=0;
70         }
71         if(!flag){cout<<"0"<<endl;continue;}
72         sort(ans,ans+anstop);
73         cout<<anstop<<endl;
74         int k;
75         for(int i=0;i<anstop;i++)
76         {
77             k=ans[i];
78             k=min(k,k^1);
79             cout<<mp2[edge[k].from].c_str()<<" "<<mp2[edge[k].to].c_str()<<endl;
80         }
81     }
82     return 0;
83 }