#include <bits/stdc++.h>
using namespace std;
#define debug(x) cerr << #x << " == " << x << endl
#define el '\n'
typedef long long ll;
const int mod = 1000000007;
const int inf = 2147483647;
const int N = 200020;
void solve()
{
	int n, m;
	cin >> n;
	vector<vector<int>> edge(n + 1);
	vector<int> f(n + 1, 0), dep(n + 1, 0), inp(n + 1, 0);
	for (int i = 1, x, y; i < n; i++) {
		cin >> x >> y;
		edge[x].push_back(y);
		edge[y].push_back(x);
		inp[x]++, inp[y]++;
	}
	int rt = 0;
	function<void(int, int)> dfs = [&](int x, int fa) {
		f[x] = fa;
		dep[x] = dep[fa] + 1;
		for (int to : edge[x]) {
			if (to == fa)
				continue;
			dfs(to, x);
		}
		if (dep[x] > dep[rt])
			rt = x;
	};
	dfs(1, 0);
	int st = rt;
	dfs(rt, 0);
	vector<int> c;
	do {
		c.push_back(rt);
		rt = f[rt];
	} while (rt);
	int cnt = 0;
	for (int i = 1; i <= n; i++) {
		if (inp[i] > 1)
			cnt++;
	}
	if (cnt <= 1) {
		cout << "-1" << el;
		return;
	}
	int mx = 1, tot = 0;
	for (int i = 1; i < c.size() - 1; i++) {
		if (i == 1 || i == c.size() - 2) {
			mx = max(mx, inp[c[i]] - 1);
			tot += inp[c[i]] - 1;
		}
		else {
			mx = max(mx, inp[c[i]] - 2);
			tot += inp[c[i]] - 2;
		}
	}
	cout << max(mx, (tot + 1) >> 1) << el;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	int T = 1;
	cin >> T;
	while (T--) {
		solve();
	}
	return 0;
}