import os
import sys
from io import BytesIO, IOBase
import threading
# 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")

# endregion

#from math import gcd,ceil,sin,radians,cos
from math import ceil
#from bisect import insort
#from collections import defaultdict as dd
def lcm(a,b):
	return (a*b)//gcd(a,b)
def inin():
	return int(input())
def inar():
	return list(map(int,input().split()))
def ar(element,size):
	return [element for i in range(size)]
def yes():
	print('Yes')
def no():
	print('No')

dx=[-1,1,0,0]
dy=[0,0,-1,1]
def dfs(i,j,visited):
	visited[i][j]=True
	for delta in range(4):
		x=j+dx[delta]
		y=i+dy[delta]
		if x>=0 and y>=0 and x<m and y<n and visited[y][x]==False:
			#print(x,y)
			if maze[y][x]=='.' or maze[y][x]=='G':
				dfs(y,x,visited)
 
Gloc=[]
Testcase=inin()
for _ in range(Testcase):
	Gloc=[]
	n,m=inar()
	maze=['' for i in range(n)]
	for i in range(n):
		maze[i]=list(input())
	pasapasi=False
	for i in range(n):
		for j in range(m):
			if maze[i][j]=='G':
				Gloc.append((i,j))
			if maze[i][j]=='B':
				for delta in range(4):
					x=j+dx[delta]
					y=i+dy[delta]
					if x>=0 and y>=0 and x<m and y<n:
						if maze[y][x]=='G':
							pasapasi=True 
							break 
						if maze[y][x]=='.':
							maze[y][x]='#'
 
	if pasapasi:
		no()
	elif maze[n-1][m-1]=="#":
		if Gloc==[]:
			yes()
		else:
			no()
	else:
 
		visited=[[False for j in range(m)] for i in range(n)]
		dfs(n-1,m-1,visited)
		cond=True
		for i,j in Gloc:
			cond = cond and visited[i][j]
		if cond:
			yes()
		else:
			no()
'''
sys.setrecursionlimit(1 << 30)
threading.stack_size(1 << 27)
 
main_thread = threading.Thread(target=main)
main_thread.start()
main_thread.join()'''