#include <iostream>
#include <string.h>
#include <vector>
#include <queue>
#include <map>
using namespace std;
int tc;
int n, X;
int head[50005], nxt[100005], to[100005], ew[100005], ecnt;
void add(int u, int v, int ww) { to[++ecnt] = v, nxt[ecnt] = head[u], head[u] = ecnt, ew[ecnt] = ww; }
int eu[50005], ev[50005];
int f[50005], g[50005];
vector<pair<int, int> > G[100005];
map<pair<int, int>, int> mp;
int deg[50005];
struct node {
    int x, dis;
};
bool vis[100005];
int dist[100005];
bool operator<(node a, node b) { return a.dis > b.dis; }
priority_queue<node> q;
void dijkstra() {
    while (!q.empty()) {
        node tmp = q.top();
        q.pop();
        int x = tmp.x;
        if (vis[x]) 
            continue;
        vis[x] = 1;
        for (auto i : G[x]) {
            int v = i.first, w = i.second;
            if (dist[v] > dist[x] + w) 
                q.push((node) { v, dist[v] = dist[x] + w });
        }
    }
}
int dep[100005], fa[100005];
void dfs(int x, int fa) {
    dep[x] = dep[fa] + 1, ::fa[x] = fa;
    for (int i = head[x]; i; i = nxt[i]) to[i] != fa ? dfs(to[i], x) : void();
}
inline int F(int x, int y) { return (f[x] == y ? g[x] : f[x]); }
int main() {
    cin >> tc;
    while (tc--) {
        memset(head, 0, sizeof head);
        memset(deg, 0, sizeof deg);
        memset(vis, 0, sizeof vis);
        ecnt = 0, mp.clear();
        dep[0] = -1;
        cin >> n >> X;
        for (int i = 1; i < n; i++) {
            int &u = eu[i], &v = ev[i];
            cin >> u >> v;
            mp[make_pair(u, v)] = i * 2 - 1;
            mp[make_pair(v, u)] = i * 2;
            add(u, v, i);
            add(v, u, i);
            ++deg[u], ++deg[v];
        }
        dfs(1, 0);
        for (int i = 1; i <= n * 2; i++) G[i].clear();
        for (int i = 1; i <= n; i++) {
            g[i] = f[i] = 0;
            for (int j = head[i]; j; j = nxt[j]) {
                if (ew[j] > ew[f[i]]) 
                    g[i] = f[i], f[i] = j;
                else if (ew[j] > ew[g[i]]) 
                    g[i] = j;
            }
            f[i] = to[f[i]];
            g[i] = to[g[i]];
            // cout << i << " " << f[i] << " asdf\n";
        }
        memset(dist, 63, sizeof dist);
        for (int i = 1; i <= n; i++) {
            for (int j = head[i]; j; j = nxt[j]) {
                int v = to[j];
                if (deg[v] == 1) {
                    int x = mp[make_pair(i, v)];
                    q.push((node) { x, dist[x] = 0 });
                } else {
                    int w = F(v, i);
                    // cout << v << " " << i << " " << F(v, i) << "\n";
                    G[mp[make_pair(v, w)]].emplace_back(make_pair(mp[make_pair(i, v)], 1));
                    if (f[w] == v) 
                        G[mp[make_pair(w, v)]].emplace_back(make_pair(mp[make_pair(i, v)], 4));
                }
            }
        }
        dijkstra();
        // for (int i = 1; i < n; i++) cout << eu[i] << " " << ev[i] <<" " << dist[mp[make_pair(eu[i], ev[i])]] << "\n";
        // for (int i = 1; i < n; i++) cout << ev[i] << " " << eu[i] <<" " << dist[mp[make_pair(ev[i], eu[i])]] << "\n";
        int p = X, ans = n + 1;
        for (int i = 0; i <= n; i++) {
            for (int j = head[p]; j; j = nxt[j]) {
                int v = to[j];
                if (fa[p] == v && dep[v] <= i) 
                    ans = min(ans, dist[mp[make_pair(v, p)]] + i);
                if (fa[p] != v && dep[v] + 1 <= i) 
                    ans = min(ans, dist[mp[make_pair(v, p)]] + i);
                // if (dep[v] + (fa[p] != v) <= i + 1) 
                //     ans = min(ans, dist[mp[make_pair(v, p)]] + i);
            }
            p = f[p];
        }
        cout << ans << "\n";
    }
    return 0;
}