#include<bits/stdc++.h>
using namespace std;
const int N = 2e5+5;
inline int read(){
	int s = 0;char ch = getchar();
	while(!isdigit(ch))ch = getchar();
	while(isdigit(ch)){s = (s<<1)+(s<<3)+ch-'0';ch = getchar();}
	return s;
}
int T,n,hd[N],ect,s,m,fa[N],odis,ans,dep[N],dis[N],mnd,mxd;
bool vis[N];
vector<int> vst[N];
struct E{
	int v,nt;
}e[2*N];
void add(int u,int v){
	e[ect].v = v;
	e[ect].nt = hd[u];
	hd[u] = ect++;
}
void dfs0(int p){
	for(int i = hd[p];i;i = e[i].nt){
		if(e[i].v!=fa[p]){
			dep[e[i].v] = dep[p]+1;
			fa[e[i].v] = p;
			dfs0(e[i].v);
		}
	}
}
void dfs1(int p,int fr){
	bool fg = 0;
	for(int i = hd[p];i;i = e[i].nt){
		if(e[i].v!=fr){
			fg = 1;
			dis[e[i].v] = dis[p]+1;
			dfs1(e[i].v,p);
		}
	}
	mxd = max(mxd,dis[p]);
	if(!fg)vst[dis[p]].emplace_back(p);
}
int tag(int p){
	int res = 0;
	mnd = min(mnd,dis[p]-dep[p]);
	while(!vis[p]){
		if(p==m)return -1;
		vis[p] = 1;
		res++;
		p = fa[p];
	}
	return res<<1;
}
int main(){
	T = read();
	while(T--){
		n = read();s = read();m = read();
		memset(hd,0,4*n+4);
		memset(vis,0,n+1);
		ect = 2;
		vis[s] = 1;
		dep[s] = dis[m] = odis = mxd = 0;
		for(int i = 1,u,v;i<n;i++){
			u = read();v = read();
			add(u,v);add(v,u);
			vst[i].clear();
		}
		fa[s] = 0;//!!!!!
		dfs0(s);dfs1(m,0);
		mnd = dis[s];
		ans = dep[m]+mxd;
//		for(int i = 1;i<=n;i++){
//			printf("%d %d\n",dis[i],dep[i]);
//		}
		for(int d = n-1,x = 0;d>0;d--){
			for(auto p:vst[d]){
				x = tag(p);
				if(~x)odis+=x;
				else break;
			}
			if(x==-1)break;
			ans = min(ans,odis+mnd+d-1);
		}
		printf("%d\n",ans);
	}
	return 0;
}