import os, sys
from io import IOBase, BytesIO
py2 = round(0.5)
if py2:
    from future_builtins import ascii, filter, hex, map, oct, zip
    range = xrange
BUFSIZE = 8192
class FastIO(BytesIO):
    newlines = 0
 
    def __init__(self, file):
        self._file = file
        self._fd = file.fileno()
        self.writable = "x" in file.mode or "w" in file.mode
        self.write = super(FastIO, self).write if self.writable else None
 
    def _fill(self):
        s = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
        self.seek((self.tell(), self.seek(0,2), super(FastIO, self).write(s))[0])
        return s
 
    def read(self):
        while self._fill(): pass
        return super(FastIO,self).read()
 
    def readline(self):
        while self.newlines == 0:
            s = self._fill(); self.newlines = s.count(b"\n") + (not s)
        self.newlines -= 1
        return super(FastIO, self).readline()
 
    def flush(self):
        if self.writable:
            os.write(self._fd, self.getvalue())
            self.truncate(0), self.seek(0)
 
class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        if py2:
            self.write = self.buffer.write
            self.read = self.buffer.read
            self.readline = self.buffer.readline
        else:
            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')
 
# Cout implemented in Python
import sys
class ostream:
    def __lshift__(self,a):
        sys.stdout.write(str(a))
        return self
cout = ostream()
endl = '\n'

t=int(input())
from collections import defaultdict
def vb():
	for i in range(n):
		for j in range(m):
			if ma[i][j]=="B":
				if i>0 and ma[i-1][j]=="G":
					return(False)
				if i>0 and ma[i-1][j]==".":
					ma[i-1][j]="#"

				if i<n-1 and ma[i+1][j]=="G":
					return(False)
				if i<n-1 and ma[i+1][j]==".":
					ma[i+1][j]="#"

				if j>0 and ma[i][j-1]=="G":
					return(False)
				if j>0 and ma[i][j-1]==".":
					ma[i][j-1]="#"

				if j<m-1 and ma[i][j+1]=="G":
					return(False)
				if j<m-1 and ma[i][j+1]==".":
					ma[i][j+1]="#"
	if ma[n-1][m-1]=="#" and gg!=0:
		return(False)
	return(True)

for _ in range(t):
	n,m=map(int,input().split())
	ma=[]
	gg=0
	for i in range(n):
		c=list(str(input()))
		gg+=c.count("G")
		ma.append(c)
	if not vb():
		print("NO")
		continue
	g=0
	v=defaultdict(lambda :False)
	s=[(n-1,m-1)]
	while s:
		x,y=s.pop()
		if v[(x,y)]:continue
		v[(x,y)]=True
		if ma[x][y]=="G":
			g+=1
		if x+1<n and ma[x+1][y]!="#":
			s.append((x+1,y))
		if x-1>-1 and ma[x-1][y]!="#":
			s.append((x-1,y))
		if y+1<m and ma[x][y+1]!="#":
			s.append((x,y+1))
		if y-1>-1 and ma[x][y-1]!="#":
			s.append((x,y-1))
	if g==gg:
		print("YES")
	else:
		print("NO")
