"""
NTC here
"""
 
 
#!/usr/bin/env python
import os
import sys
from io import BytesIO, IOBase

profile = 0
pypy = 1
 
 
def iin(): return int(input())


def lin(): return list(map(int, input().split()))


 
def main():
    T = iin()
    dc = {'.':0, '#':1, 'G':2, 'B':3}
    while T:
        T-=1
        n, m = lin()
        a = [[dc[j] for j in input()] for i in range(n)]
        # print(a)
        for i in range(n):
            for j in range(m):
                if a[i][j] == 3:
                    if i>0 and a[i-1][j] == 0:
                        a[i-1][j] = 1
                    if j>0 and a[i][j-1] == 0:
                        a[i][j-1] = 1
                    if i<n-1 and a[i+1][j] == 0:
                        a[i+1][j] = 1
                    if j<m-1 and a[i][j+1] == 0:
                        a[i][j+1] = 1
        # print(a)
        # find path
        dp = [[0]*m for i in range(n)]
        dp[n-1][m-1] = 1 if a[n-1][m-1] == 0 else 0
        for i in range(n-1, -1, -1):
            for j in range(m-1, -1, -1):
                if a[i][j] == 1:
                    continue
                if i>0 and a[i-1][j] != 1:
                    dp[i][j] += dp[i-1][j]
                if j>0 and a[i][j-1] != 1:
                    dp[i][j] += dp[i][j-1]
                if i<n-1 and a[i+1][j] != 1:
                    dp[i][j] += dp[i+1][j]
                if j<m-1 and a[i][j+1] != 1:
                    dp[i][j] += dp[i][j+1]
        ans = True
        for i in range(n):
            for j in range(m):
                if a[i][j] == 2:
                    if dp[i][j] == 0:
                        ans = False
                elif a[i][j] == 3:
                    if dp[i][j] != 0:
                        ans = False
        # print(dp)
        print('Yes' if ans else 'No')






                

        

 
 
 
 
 
 
# 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")
 
if pypy:
    sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
    input = lambda: sys.stdin.readline().rstrip("\r\n")
 
# endregion
 
if __name__ == "__main__":
    if profile:
        import cProfile
        cProfile.run('main()')
    else:
        main()