//In the name of God
#include<bits/stdc++.h>
/*MHN*/
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
using namespace std;
typedef long long int lli;
typedef long double ld;
typedef pair<lli,lli> pii;
typedef vector<lli> ve;
typedef vector<pii> vp;
const lli N=4e5+100;
const lli mod=1e9+7;//998244353;
const lli INF=1e18;
lli power(lli x,lli y){lli res = 1;x = x % mod;while(y>0){if( y & 1 ){res = (res * x) % mod;}y = y >> 1;x = (x * x)%mod;}return res;}
lli modinv(lli x){return power(x,mod-2);}
lli divide(lli x,lli y){return ((x%mod) * modinv(y))%mod;}
lli Tarkib(lli n, lli r){if(n<r)return 0;if(r==0)return 1;if(n-r < r)return Tarkib(n,n-r);lli res = 1;for(lli i = r; i >= 1; i--)res = divide(((res%mod) * (n-i+1))%mod,i);return res;}
#define all(v) v.begin(),v.end()
#define MIN(v) *min_element(all(v))
#define MAX(v) *max_element(all(v))
#define migmig ios_base::sync_with_stdio(false),cout.tie(0), cin.tie(0);
#define read freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define set_preci(x) cout << fixed << setprecision(x);
#define debug(x) cerr << (#x) << " " << (x) << endl
#define MP make_pair
#define PB push_back
#define fi first
#define se second
#define SUM(v) accumulate(v.begin(),v.end(), 0LL)
#define FOR(x,n) for(lli x = 0; x < n; x++)
#define FORS(x,n) for(lli x = 1; x <= n; x++)
#define TEST int T; cin>>T;while(T--)
#define BN(l,a) while(l){a.PB(l%2);l/=2;}
#define lb lower_bound
#define ub upper_bound
#define endl "\n"
#define sep " "
lli tmp;
set<lli> v[N];
lli deg[N];
lli n;
bool vis[N];
ve leaf;
void dfs(lli u){
    vis[u] = 1;
    if(deg[u]==1 && tmp < 2){
        leaf.PB(u);
        tmp ++;
    }
    if(deg[u]==0){
        leaf.PB(u);
        leaf.PB(u);
    }
    for(auto i : v[u]){
        if(vis[i])
            continue;
        dfs(i);
    }
}
int main(){
    migmig;
    TEST{
        cin>>n;
        FOR(i,n-1){
            lli a,b;
            cin>>a>>b;
            v[a].insert(b);
            v[b].insert(a);
            deg[a]++;
            deg[b]++;
        }
        lli del = 0;
        vp p1;
        FORS(i,n){
            vp g;
            for(auto u : v[i]){
                if(deg[i]<=2)
                    break;
                if(deg[u]<=2)
                    break;
                del++;
                deg[i]--;
                deg[u]--;
                g.PB(MP(i,u));
                p1.PB(MP(i,u));
            }
            for(auto u : g){
                v[u.fi].erase(v[u.fi].find(u.se));
                v[u.se].erase(v[u.se].find(u.fi));
            }
        }
        FORS(i,n){
            vp g;
            for(auto u : v[i]){
                if(deg[i]<=2)
                    break;
                if(deg[u]<=1)
                    break;
                del++;
                deg[i]--;
                deg[u]--;
                g.PB(MP(i,u));
                p1.PB(MP(i,u));
            }
            for(auto u : g){
                v[u.fi].erase(v[u.fi].find(u.se));
                v[u.se].erase(v[u.se].find(u.fi));
            }
        }
        FORS(i,n){
            vp g;
            for(auto u : v[i]){
                if(deg[i]<=2)
                    break;
                del++;
                deg[i]--;
                deg[u]--;
                g.PB(MP(i,u));
                p1.PB(MP(i,u));
            }
            for(auto u : g){
                v[u.fi].erase(v[u.fi].find(u.se));
                v[u.se].erase(v[u.se].find(u.fi));
            }
        }
        FORS(i,n){
            if(vis[i])
                continue;
            dfs(i);
            tmp = 0;
        }
        vp p2;
        lli s = leaf.size();
        FORS(i,s-2){
            p2.PB(MP(leaf[i],leaf[i+1]));
            i ++;
        }
        cout<<del<<endl;
        FOR(i,del){
            cout<<p1[i].fi<<sep<<p1[i].se<<sep<<p2[i].fi<<sep<<p2[i].se<<endl;
        }
        FORS(i,n){
            v[i].clear();
            vis[i] = 0;
            deg[i] = 0;
        }
        leaf.clear();
    }
}