#include<bits/stdc++.h>
using namespace std;
const int MAXN=5e4+5;
unordered_map <int,int> d[MAXN];
vector <int> G[MAXN];
int n,f[MAXN],g[MAXN],dep[MAXN],up[MAXN][20],L[MAXN],R[MAXN],dcnt;
void dfs(int u,int fz) {
	L[u]=++dcnt,up[u][0]=fz,dep[u]=dep[fz]+1;
	for(int k=1;k<20;++k) up[u][k]=up[up[u][k-1]][k-1];
	vector <int> e;
	for(int v:G[u]) if(v^fz) dfs(v,u),e.push_back(v);
	R[u]=dcnt,G[u].swap(e);
}
int nxt(int s,int t) { //s->t
	if(L[t]<L[s]||R[s]<L[t]) return up[s][0];
	return *lower_bound(G[s].begin(),G[s].end(),t,[&](int x,int y){ return R[x]<R[y]; });
}
void solve() {
	int X;
	scanf("%d%d",&n,&X);
	for(int i=1;i<=n;++i) f[i]=g[i]=0,G[i].clear(),d[i].clear();
	for(int i=1,u,v;i<n;++i) {
		scanf("%d%d",&u,&v);
		G[u].push_back(v),G[v].push_back(u);
		g[u]=f[u],f[u]=v,g[v]=f[v],f[v]=u;
	}
	dcnt=0,dfs(1,0);
	queue <array<int,2>> q;
	d[1][f[X]^1?f[X]:g[X]]=0;
	q.push({1,f[X]^1?f[X]:g[X]});
	while(q.size()) {
		int u=q.front()[0],v=q.front()[1],dis=d[u][v]; q.pop();
		if(!v) return printf("%d\n",dis),void();
		auto ext=[&](int x,int y) {
			if(!d[x].count(y)) d[x][y]=dis+1,q.push({x,y});
		};
		if(u==f[v]) ext(u,g[v]),ext(v,u),ext(f[u],u);
		else {
			int z=nxt(u,v);
			if(z==f[v]) ext(z,g[v]),ext(u,z);
			else ext(z,f[v]);
		}
	}
}
signed main() {
	freopen("toptree.in","r",stdin);
	freopen("toptree.out","w",stdout);
	int T; scanf("%d",&T);
	while(T--) solve();
	return 0;
}