# -*- coding: utf-8 -*-
"""
Created on Sun Jun  7 20:52:33 2020

@author: Mridul Garg
"""
from collections import deque
q = int(input())
for _ in range(q):
    n, m = list(map(int, input().split(" ")))
    
    A = []
    for i in range(n):
        A.append(list(input()))
        
    
    see = False            
    for i in range(n):
        for j in range(m):
            if A[i][j] == "G":
                see = True
    if see == False:
        print("Yes")
        continue
        
    def CHECK(i, j):
        if i > 0:
            if A[i-1][j] == "G":
                return -1
            elif A[i-1][j] != "B":
                A[i-1][j] = "#"
        
        if i < n-1:
            if A[i+1][j] == "G":
                return -1
            elif A[i+1][j] != "B":
                A[i+1][j] = "#"
                
        if j > 0:
            if A[i][j-1] == "G":
                return -1
            elif A[i][j-1] != "B":
                A[i][j-1] = "#"
        if j < m-1:
            if A[i][j+1] == "G":
                return -1
            elif A[i][j+1] != "B":
                A[i][j+1] = "#"
                
    done = False    
    for i in range(n):
        if done == True:
            break
        for j in range(m):
            if A[i][j] == "B":
                c = CHECK(i, j)
                if c == -1:
                    done = True
                    break
                
    if done == True:
        print("No")
        continue
    if A[n-1][m-1] in "#B":
        print("No")
        continue
    
    G = {}
    col = {}
    
    for i in range(n):
        for j in range(m):
            if A[i][j] not in "#B":
            
                key = (i, j)
                G[key] = []
                col[key] = "w"
                
                if i > 0:
                    if A[i-1][j] not in "#B":
                        G[key].append((i-1, j))
                
                if i < n-1:
                    if A[i+1][j] not in "#B":
                        
                        G[key].append((i+1, j))
                        
                if j > 0:
                    if A[i][j-1] not in "#B":
                        
                        G[key].append((i, j-1))
                if j < m-1:
                    if A[i][j+1] not in "#B":
                        
                        G[key].append((i, j+1))
                    
    Q = deque([])
    
    Q.append((n-1, m-1))
    while len(Q) != 0:
        u = Q.popleft()
        l = G[u]
        for v in l:
            if col[v] == "w":
                col[v] = "b"
                Q.append(v)
        col[u] = "b"

    for i in range(n):
        if done:
            break
        for j in range(m):
            if A[i][j] == "G":
                if col[(i, j)] != "b":
                    done = True
                    break
                
    if done:
        print("No")
    else:
        print("Yes")
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    