#include<cstdio>
using namespace std;
const int N = 6e5 + 10;
int n, ansa[N], ansb[N], d[N], p[N];

int tot = 0, head[N], ver[N], pre[N];
void add(int u, int v) {
    ver[++tot] = v, pre[tot] = head[u], head[u] = tot;
}

int cnt = 0;
void init() {
    for(int i = 1; i <= tot; i++) {
        ver[i] = 0, pre[i] = 0;
    }
    for(int i = 1; i <= n; i++) {
        d[i] = 0, p[i] = 0, ansa[i] = 0, ansb[i] = 0, head[i] = 0;
    }
    tot = 0;
    cnt = 0;
}

void dfs(int u, int fa) {
    int a = 0;
    p[u] = u;
    for(int i = head[u]; i; i = pre[i]){
        int v = ver[i];
        if(v == fa) continue;
        dfs(v, u);
        if(a == 0) a = p[v];
        else {
            ++cnt;
            ansa[cnt] = a;
            ansb[cnt] = p[v];
            a = 0;  
        }
    }
    if(a) p[u] = a;
}
void solve() {
    scanf("%d", &n);
    for(int i = 1; i < n; i++) {
        int u, v;
        scanf("%d%d", &u, &v);
        add(u, v);
        add(v, u);
        d[u]++, d[v]++;
    }
    int root = 0;
    for(int i = 1; i <= n; i++) {
        if(d[i] % 2 == 0) {
            root = i;
            break;
        }
    }
    if(!root) {
        puts("-1");
        return;
    }
    dfs(root, 0);
    printf("%d\n", cnt);
    for(int i = 1; i <= cnt; i++) {
        printf("%d %d\n", ansa[i], ansb[i]);
    }
}

int main() {
    int T;
    scanf("%d", &T);
    while(T--) {
        init();
        solve();
    }
    return 0;
}