#pragma GCC optimize("-Ofast", "-finline", "-funroll-loops", "-fno-stack-protector")
#include <bits/stdc++.h>
#define rep(i,l,r) for (int i(l), i##end(r); i <= i##end; ++i)
#define per(i,r,l) for (int i(r), i##end(l); i >= i##end; --i)
using namespace std;
bool _Mbe; int subtask_id; char ibuf[1 << 25], *iS, *iT;
#define getc() (iS == iT ? iT = (iS = ibuf) + fread(ibuf, 1, 1 << 25, stdin), (iS == iT ? EOF : *iS++) : *iS++)
template <typename T> inline void read(T &x) { x = 0; bool f = 0; char ch = getc(); while (ch < '0' || ch > '9') f ^= ch == '-', ch = getc(); while (ch <= '9' && ch >= '0') x = x * 10 + ch - '0', ch = getc(); if (f) x = -x;}
template <typename Tx, typename ...Ty> inline void read(Tx &x, Ty &...y) { read(x); read(y...);}
template <typename T> inline void Write(T x) { if (x > 9) Write(x / 10); putchar(x % 10 + '0');}
template <typename T> inline void write(T x, char ch = '\n') { if (x < 0) { putchar('-'); x = -x;} Write(x); putchar(ch);}
template <typename T> inline void cmin(T &x, T y) { (x > y) && (x = y);}
template <typename T> inline void cmax(T &x, T y) { (x < y) && (x = y);}
#define File(filename) freopen(filename ".in", "r", stdin), freopen(filename ".out", "w", stdout)

/* - - - all above template - - - */
#define PII pair <int, int>

const int N = 5e4 + 9;
const int Ecnt = N * 4;
const int inf = 1e9;
int n, x, ecnt(1);
int head[N], dep[N], fa[N], suf[N][2];
int dis[Ecnt];
struct Edge {int from, to, nxt; } e[Ecnt];

priority_queue <PII, vector <PII>, greater<PII> > pq;

void add_edge(int u, int v) {
    e[++ecnt] = (Edge) {u, v, head[u]};
    head[u] = ecnt;
}

// 返回的是边的编号
int F(int x, int u) {return suf[x][e[suf[x][0]].to == u];}

void dfs(int u, int lst) {
    fa[u] = lst;
    for (int i = head[u]; i; i = e[i].nxt) {
        if (int v = e[i].to; v != lst) {
            dep[v] = dep[u] + 1;
            dfs(v, u);
        }
    }
}

void upd(int u, int v) {
    if (dis[u] > v) {
        // printf("    id = %d, u = %d, x = %d, dis = %d\n", u, e[u].from, e[u].to, v);
        dis[u] = v;
        pq.push(make_pair(v, u));
    }
}

void skymaths() {
    read(n, x);

    ecnt = 1; memset(head, 0, sizeof(head[0]) * (n + 1));

    for (int i = 1, u, v; i < n; ++i) {
        read(u, v);
        add_edge(u, v); add_edge(v, u);
    }
    dfs(1, 0);
    rep (i, 1, n) {
        suf[i][0] = suf[i][1] = 0;
        for (int j = head[i], t = 0; j && t < 2; j = e[j].nxt) {
            // 因为这本身是降序的
            suf[i][t++] = j;
        }
    }

    // 代表 u 在 from，x 在 to

    fill(dis + 1, dis + ecnt + 1, inf);
    dis[0] = -inf;
    int X = x;
    rep (i, 0, 2 * n) {
        int to = e[suf[X][0]].to;
        if ((to == fa[X] && dep[to] <= i) || (to != fa[X] && dep[to] + 1 <= i)) {
            upd(suf[X][0] ^ 1, i);
        }
        X = to;
    }

    while (!pq.empty()) {
        PII top = pq.top(); pq.pop();
        int s = top.second; if (dis[s] != top.first) continue;
        int u = e[s].from;
        int x = e[s].to;
        int id = F(x, u); int w = e[id].to;
        upd(id, dis[s] + 1);
        if (F(x, x) == id && F(w, w) == (id ^ 1)) upd(id ^ 1, dis[s] + 4);
    }

    int ans(inf);
    rep (i, 2, ecnt) {
        if (F(e[i].to, e[i].from) == 0) {
            // cerr << "End id = " << i << endl;
            cmin(ans, dis[i]);
        }
    }

    printf("%d\n", ans);
}

/*
start coding
at 21:17
finish coding
finish debugging
*/

bool _Med; double start_time;
signed main() {
    start_time = clock();
    cerr << "memories= " << (&_Mbe - &_Med) / 1048576.0 << "MiB" << endl;

/*
#ifdef DEBUG
    freopen("a.in", "r", stdin);
#else
    File("toptree");
#endif
*/
    int T = 1;
    scanf("%d", &T);
    while (T--) {
        skymaths();
    }

    cerr << "time= " << (clock() - start_time) / CLOCKS_PER_SEC << "sec" << endl;
    return 0;
}