# May the Speedforce be with us...
'''
problem statement achhe se padhna hai
age se bhi dekhna hai, piche se bhi dekhna hai
'''
#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')
'''
def countDivisibles(A, B, M): #count numbers in the range[A,B] which are divisible by M
    if (A % M == 0): 
        return ((B // M) - (A // M)) + 1
    return ((B // M) - (A // M)) 
	
def  countSetBits(n): #count the number of set bits in the binary representation of an integer
    count = 0
    while (n): 
        count += n & 1
        n >>= 1
    return count
def digitsum(num): #return the sum of dogots of a number
	su=0
	while(num):
		su+=num%10
		num//=10
	return su
'''




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()
		











	
	
	
