#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000000;
int nxi() {
  int a;
  cin >> a;
  return a;
}
vector<long long> a;
void inc(int i, long long v) {
  for (; i < a.size(); i |= i + 1) {
    a[i] = max(a[i], v);
  }
}
long long get(int r) {
  long long ans = 0;
  for (; r >= 0; r = (r & (r + 1)) - 1) {
    ans = max(ans, a[r]);
  }
  return ans;
}
long long get(int l, int r) { return get(r) - get(l - 1); }
template <class _T>
_T gcd(_T a, _T b) {
  return a == 0 ? b : gcd(b % a, a);
}
long long bin_pow(long long a, long long p) {
  long long res = 1;
  while (p > 0) {
    if (p & 1) res = (res * a) % 1000000007;
    p /= 2;
    a = (a * a) % 1000000007;
  }
  return res;
}
int main() {
  ios_base::sync_with_stdio(0);
  int tst = nxi();
  for (int _test = 0; _test < tst; _test++) {
    int n = nxi(), m = nxi();
    int b_count = 0;
    int g_count = 0;
    vector<string> mp(n + 2);
    mp[0] = string(m + 2, '#');
    mp[n + 1] = mp[0];
    vector<pair<int, int> > bads, goods;
    for (int i = 1; i <= n; i++) {
      string& s = mp[i];
      cin >> s;
      s = "#" + s + "#";
      for (int j = 0; j <= m; j++) {
        if (s[j] == 'G') {
          goods.push_back(make_pair(i, j));
        }
        if (s[j] == 'B') {
          bads.push_back(make_pair(i, j));
        }
      }
    }
    g_count = goods.size();
    if (g_count == 0) {
      cout << "Yes\n";
      continue;
    }
    int dx[] = {0, 1, 0, -1};
    bool answer = true;
    for (auto bad : bads) {
      for (int i = 0; i < 4; i++) {
        int nx = bad.first + dx[i], ny = bad.second + dx[(i + 1) % 4];
        if (mp[nx][ny] == 'G') {
          answer = false;
        } else if (mp[nx][ny] == 'B') {
          continue;
        } else {
          mp[nx][ny] = '#';
        }
      }
    }
    vector<vector<int> > visited(n + 2, vector<int>(m + 2));
    answer &= mp[n][m] != '#';
    if (answer) {
      queue<pair<int, int> > q;
      q.push(make_pair(n, m));
      visited[n][m] = 1;
      while (!q.empty()) {
        pair<int, int> cur = q.front();
        q.pop();
        for (int i = 0; i < 4; i++) {
          int nx = cur.first + dx[i], ny = cur.second + dx[(i + 1) % 4];
          if (mp[nx][ny] != '#' && !visited[nx][ny]) {
            visited[nx][ny] = 1;
            q.push(make_pair(nx, ny));
          }
        }
      }
      for (pair<int, int> good : goods) {
        answer &= visited[good.first][good.second];
      }
      for (pair<int, int> bad : bads) {
        answer &= !visited[bad.first][bad.second];
      }
    }
    cout << (answer ? "Yes" : "No") << endl;
  }
  return 0;
}
