#!/usr/bin/env python
import os
import sys
from io import BytesIO, IOBase
import threading 


def main(n,m,grid):
    delta=[(1,0),(0,1),(-1,0),(0,-1)]
    g_cnt=0
    for i in range(n):
        for j in range(m):
            if grid[i][j]=='B':
                for d_x ,d_y in delta :
                    n_x=i+d_x
                    n_y=j+d_y
                    if 0<=n_x<n and 0<=n_y<m :
                        if grid[n_x][n_y]=='.':
                            grid[n_x][n_y]='#'
                        if grid[n_x][n_y]=='G':
                            return 'No'
            elif grid[i][j]=='G':
                g_cnt+=1

    

    q=[]
    eg_cnt=0
    if grid[n-1][m-1]!='#':
        q.append((n-1,m-1))
    while len(q):
        # print(q)
        x,y=q.pop()
        if grid[x][y]=='G':
            eg_cnt+=1
        grid[x][y]='#'
        for d_x ,d_y in delta :
            n_x=x+d_x
            n_y=y+d_y

            if 0<=n_x<n and 0<=n_y<m and grid[n_x][n_y] in ('.','G'):
                q.append((n_x,n_y))
    
    if eg_cnt==g_cnt:
        return('Yes')
    else:
        return('No')



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")

# endregion

if __name__ == "__main__":
    for _ in range(int(input())):
        n,m=map(int,input().split())
        grid=[]
        for i in range(n):
            grid.append([c for c in input()])

        print(main(n,m,grid))
