#pragma GCC optimize(2)
#include <bits/stdc++.h>
#define MAXN 200005
#define For(I,A,B) for(int I = (A), endi = (B); I <= endi; ++I)
#define foR(I,A,B) for(int I = (A), endi = (B); I >= endi; --I)
#define ForE(I,A) for(int I = head[A]; I; I = e[I].nxt)
using namespace std;
typedef long long _ll;
typedef unsigned int ui;

struct Edge { int to,nxt; } e[MAXN<<1];
int head[MAXN],tot;
void add_edge(int x,int y) { e[++tot] = (Edge){y,head[x]}; head[x] = tot; }

int T,mx,ans,cnt,dis,n,m,s,u,v,dep[MAXN],pre[MAXN];
bool hasS[MAXN],inS[MAXN];
void dfs(int u, int prev)
{
    pre[u] = prev;
    if(u == s) hasS[u] = 1;
    ForE(i,u)
    {
        int v = e[i].to;
        if(v == prev) continue;
        dep[v] = dep[u] + 1;
        dfs(v,u);
        if(hasS[v]) hasS[u] = 1;
    }
}
void dfs2(int u, int pre)
{
    inS[u] = 1;
    ForE(i,u)
    {
        int v = e[i].to;
        if(v == pre) continue;
        dfs2(v,u);
    }
}
void dfs3(int u, int pre)
{
    ++cnt;
    dis = max(dis,dep[u]);
    ForE(i,u)
    {
        int v = e[i].to;
        if(v == pre) continue;
        dfs3(v,u);
    }
}
void solve()
{
    cin >> n >> s >> m; mx = ans = 0;
    tot = 0; fill(head,head+n+1,0); 
    fill(hasS,hasS+n+1,0); fill(dep,dep+n+1,0); fill(inS,inS+n+1,0);
    For(i,2,n) cin >> u >> v, add_edge(u,v), add_edge(v,u);
    dfs(m,0); 
    ForE(i,m)
        if(hasS[e[i].to]) 
            dfs2(e[i].to,m);
    For(i,1,n) if(!inS[i]) mx = max(mx,dep[s]+dep[i]);
    u = s; ans = mx;
    if(s == m)
    {
        For(i,1,n) ans = max(ans,dep[i]);
        cout << ans << '\n';
        return;
    }
    do
    {
        dis = cnt = 0;
        ForE(i,u)
        {
            int v = e[i].to;
            if(v != pre[u] && !hasS[v]) dfs3(v,u);
        }
        ans = max(ans,min(dis+dep[s],cnt*2+mx));
        u = pre[u];
    }while(u != m);
    cout << max(ans,mx) << '\n';
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    cin >> T;
    while(T--) solve();
    return 0;
}