//Cut it out, you've already lost.
#include<bits/stdc++.h>
using namespace std;
const int maxn=500005;
int n,m,T;
vector<int>v[maxn];
vector< pair<int,int> >ans;
int dfs(int x,int last){
	int res=0;
	for(int i=0;i<v[x].size();i++){
		int y=v[x][i];
		if(y==last)
			continue;
		int ret=dfs(y,x);
		if(ret){
			if(res){
				ans.emplace_back(make_pair(res,ret));
				res=0;
			}
			else res=ret;
		}
	}
	if(res==0)
		return x;
	return res;
}
int main(){
	scanf("%d",&T);
	while(T--){
		ans.clear();
		scanf("%d",&n);
		for(int i=1,x,y;i<n;i++)
			scanf("%d%d",&x,&y),v[x].emplace_back(y),v[y].emplace_back(x);
		int rt=-1;
		for(int i=1;i<=n;i++)
			if(v[i].size()%2==0)
				rt=i;
		if(rt==-1)
			puts("-1");
		else{
			dfs(rt,0);
			printf("%d\n",ans.size());
			for(int i=0;i<ans.size();i++)
				printf("%d %d\n",ans[i].first,ans[i].second);
		}
		for(int i=1;i<=n;i++)
			v[i].clear();
	}
	return 0;
}