import os
import sys
from io import BytesIO, IOBase
# region fastio

BUFSIZE = 8192

class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

# ------------------------------

from math import factorial
from collections import Counter, defaultdict, deque
from heapq import heapify, heappop, heappush

def RL(): return map(int, sys.stdin.readline().rstrip().split())
def RLL(): return list(map(int, sys.stdin.readline().rstrip().split()))
def N(): return int(input())
def comb(n, m): return factorial(n) / (factorial(m) * factorial(n - m)) if n >= m else 0
def perm(n, m): return factorial(n) // (factorial(n - m)) if n >= m else 0
def mdis(x1, y1, x2, y2): return abs(x1 - x2) + abs(y1 - y2)
mod = 998244353
INF = float('inf')

# ------------------------------


def main():
    for _ in range(N()):
        n, m = RL()
        gp = [list(input()) for _ in range(n)]
        nex = [[1, 0], [0, 1], [-1, 0], [0, -1]]
        gd = 0
        bad = 0
        tag = False

        for i in range(n):
            for j in range(m):
                if gp[i][j]=='G': gd+=1
                if gp[i][j] == 'B':
                    bad+=1
                    for xx, yy in nex:
                        if -1<xx+i<n and -1<yy+j<m and gp[xx+i][yy+j]=='.':
                            gp[xx+i][yy+j] = '#'
                        if -1 < xx + i < n and -1 < yy + j < m and gp[xx + i][yy + j] == 'G':
                            tag = True



        if gp[-1][-1]=='B' or tag:
            print('No')

        elif gp[-1][-1]=='#':
            if gd!=0:
                print('No')
            else:
                print('Yes')
        else:
            q = deque()
            q.append((n-1, m-1))
            vis = [[0]*m for _ in range(n)]
            vis[-1][-1] = 1

            if gp[n-1][m-1]=='G':
                gd-=1

            while q:
                px, py = q.popleft()
                bd = 0
                for xx, yy in nex:
                    nx, ny = xx+px, yy+py
                    if -1<nx<n and -1<ny<m and vis[nx][ny]==0:
                        vis[nx][ny] = 1
                        if gp[nx][ny] == 'G':
                            gd-=1
                        if gp[nx][ny]=='B':
                            bd+=1
                        if gp[nx][ny]=='.' or gp[nx][ny]=='G':
                            q.append((nx, ny))

            print('Yes' if gd==0 and bd==0 else 'No')






if __name__ == "__main__":
    main()

