#include<bits/stdc++.h>
using namespace std;
const int MAXN = 3e5 + 5;
vector<int> e[MAXN];
int n,d[MAXN],dep[MAXN],llf,num,exlf;
int dfn[MAXN],totdfn,st[MAXN][20],lg[MAXN];
bool del[MAXN];
struct edge
{
    int u,v;
};
vector <edge> res;
int Get(int x,int y)
{
    if(dfn[x] < dfn[y]) return x;
    else return y;
}
void build()
{
    for(int j = 1;j <= lg[n]; ++j)
        for(int i = 1; i + (1 << j) - 1 <=n; ++i)
            st[i][j] = Get(st[i][j - 1],st[i + (1 << j - 1)][j - 1]);
}
int lca(int u,int v)
{
    if(u == v) return u;
    if(dfn[u] > dfn[v]) swap(u,v);
    int k = lg[dfn[v] - dfn[u]];
    return Get(st[dfn[u] + 1][k],st[dfn[v] - (1 << k) + 1][k]);
}
void dfs(int p,int fa)
{
    dfn[p] = ++totdfn;st[totdfn][0] = fa;
    for(int v : e[p])
    {
        if(v == fa) continue;
        dfs(v,p);
    }
    
    int lst = 0;
    for(int v : e[p])
    {
        if(v == fa) continue;
        if(d[v] == 1)
        {
            if(lst)
            {
                res.push_back({lst,v});
                num -= 2;d[p] -= 2;
                del[lst] = del[v] = 1;
                lst = 0;
            }
            else lst = v;
        }
    }
}
void solve(int p,int fa)
{
    if(d[p] == 1 && p != 1)
    {
        int LCA = lca(llf,p);
        if(exlf) LCA = exlf,exlf = 0;
        res.push_back({LCA,p});
        llf = p;
    }
    sort(e[p].begin(),e[p].end(),[&](int x,int y){return d[x] < d[y];});

    // cout<<"solve p:"<<p<<endl;

    for(int v : e[p])
    {
        if(v == fa || del[v]) continue;
        solve(v,p);
    }
}
int main()
{
    for(int i = 2; i <= 300000; ++i) lg[i] = lg[i >> 1] + 1;
    int T;scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);

        for(int i = 1; i <= n; ++i)
        {
            e[i].clear();
            d[i] = 0;del[i] = 0;
        }
        num = n;llf = 1;totdfn = 0;exlf = 0;
        res.clear();

        for(int i = 1; i < n; ++i)
        {
            int u,v;scanf("%d %d",&u,&v);
            e[u].push_back(v);
            e[v].push_back(u);
            d[u]++;d[v]++;
        }

        dfs(1,0);
        build();
        for(int v : e[1])
            if(!del[v] && d[v] == 1) exlf = v,del[v] = 1;

        // cout<<"size:"<<endl;
        // cout << res.size()<<endl;

        solve(1,0);

        if(num == 2) printf("-1\n");
        else
        {
            int k = res.size();
            printf("%d\n",k);
            for(auto [u,v] : res)
                printf("%d %d\n",u,v);
        }
    }
    return 0;
}