/// orz tourist
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

__attribute__((always_inline)) void read(int &num) {
  static char inBuffer[0x30D40];
  static unsigned int p = 0x30D3F; num = 0x0;
  while(inBuffer[p] < 0x30 | inBuffer[p] > 0x39) {
    ++p != 0x30D40 || (fread(inBuffer, 0x1, 0x30D40, stdin), p = 0x0);
  }
  while(inBuffer[p] > 0x2F & inBuffer[p] < 0x3A) {
    num = num * 0xA + inBuffer[p] - 0x30;
    ++p != 0x30D40 || (fread(inBuffer, 0x1, 0x30D40, stdin), p = 0x0);
  }
}

const int N = 100000;
int n, p[N], up[N], down[N], md[N], aux_up[N];
vector<int> g[N], so[N];

void dfs1(int a) {
  int m1 = 0, m2 = 0;
  md[a] = 1;
  for (auto &b : g[a]) {
    if (b != p[a]) {
      p[b] = a;
      dfs1(b);
      md[a] = max(md[a], 1 + md[b]);
      if (md[b] > m1) {
        m2 = m1;
        m1 = md[b];
      } else {
        if (md[b] > m2) {
          m2 = md[b];
        }
      }
    }
  }
  down[a] = m1 + m2 + 1;
}

void dfs2(int a) {
  so[a].clear();
  for (auto &b : g[a]) {
    if (b != p[a]) {
      so[a].push_back(md[b]);
    }
  }
  sort(so[a].rbegin(), so[a].rend());
  up[a] = 0;
  if (a) {
    int v1 = 0;
    int v2 = 1;
    v1 = 1 + aux_up[p[a]];
    if ((int) so[p[a]].size() >= 2) {
      if (md[a] == so[p[a]][0]) {
        v1 = max(v1, so[p[a]][1] + 2);
      } else {
        v1 = max(v1, so[p[a]][0] + 2);
      }
    }
    if ((int) so[p[a]].size() == 2) {
      if (md[a] == so[p[a]][0]) {
        v2 = so[p[a]][1] + 1;
      } else {
        v2 = so[p[a]][0] + 1;
      }
    }
    if ((int) so[p[a]].size() >= 3) {
      int x = so[p[a]][0];
      int y = so[p[a]][1];
      int z = so[p[a]][2];
      if (md[a] == x) {
        v2 = y + z + 1;
      } else {
        if (md[a] == y) {
          v2 = x + z + 1;
        } else {
          v2 = x + y + 1;
        }
      }
    }
    aux_up[a] = v1;
    up[a] = v2;
  }
  up[a] = max(aux_up[a] - 1, up[a]);
  for (auto &b : g[a]) {
    if (b != p[a]) {
      dfs2(b);
    }
  }
}

int main() {
  freopen ("revolta.in", "r", stdin);
  freopen ("revolta.out", "w", stdout);

  aux_up[0] = 1;
  p[0] = -1;
  int t;
  read(t);
  for (int tc = 0; tc < t; tc++) {
    read(n);
    for (int i = 0; i < n; i++) {
      g[i].clear();
    }
    for (int i = 0; i < n - 1; i++) {
      int a, b;
      read(a);
      read(b);
      g[a].push_back(b);
      g[b].push_back(a);
    }
    dfs1(0);
    dfs2(0);
    int sol = (1 << 30);
    for (int i = 0; i < n; i++) {
      int d1 = up[i];
      int d2 = down[i];
      int cur = max(d1 / 2 + d2 / 2 + 2, max(d1, d2)) - 1;
      sol = min(sol, cur);
    }
    printf("%d\n", sol);
  }
}