#include<bits/stdc++.h>
using namespace std;
const int N=3e5+5;
vector<int> gr[N];
int n,deg[N],up[N];
vector<pair<int,int>> ans;
void dfs(int u,int fa){
    vector<int> son;
    for(auto v:gr[u]){
        if(v==fa)continue;
        dfs(v,u);
        son.push_back(v);
    }
    if(son.size()%2==0){
        for(int i=0;i+1<son.size();i+=2){
            ans.push_back(make_pair(up[son[i]],up[son[i+1]]));
        }
        up[u]=u;
    }else{
        up[u]=up[son[0]];
        for(int i=1;i+1<son.size();i+=2){
            ans.push_back(make_pair(up[son[i]],up[son[i+1]]));
        }
    }
}
void solve(){
    cin>>n;
    for(int i=1;i<n;i++){
        int u,v;
        cin>>u>>v;
        deg[u]++;
        deg[v]++;
        gr[u].push_back(v);
        gr[v].push_back(u);
    }
    int rt=0;
    for(int i=1;i<=n;i++){
        if(deg[i]%2==0){
            rt=i;
            break;
        }
    }
    if(rt==0){
        cout<<-1<<'\n';
    }else{
        dfs(rt,0);
        cout<<ans.size()<<'\n';
        for(auto p:ans){
            cout<<p.first<<" "<<p.second<<'\n';
        }
    }
    for(int i=1;i<=n;i++){
        deg[i]=0;
        gr[i].clear();
    }
    ans.clear();
}
int main(){
    //freopen("test.in","r",stdin);
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int T;
    cin>>T;
    while(T--){
        solve();
    }
    return 0;
}