#------------------------------warmup----------------------------
import os
import sys
import math
from io import BytesIO, IOBase
from fractions import Fraction
 
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")
 
#-------------------game starts now----------------------------------------------------
for t in range (int(input())):
    n,m=map(int,input().split())
    a=[['.' for i in range (m)]for j in range (n)]
    for i in range (n):
        s=input()
        for j in range (m):
            a[i][j]=s[j]
    ch=1
    for i in range (n):
        for j in range (m):
            if a[i][j]=='B':
                if i!=0 and a[i-1][j]!='B' and a[i-1][j]!='B':
                    a[i-1][j]='#'
                if i!=n-1 and a[i+1][j]!='B' and a[i+1][j]!='B':
                    a[i+1][j]='#'
                if j!=0 and a[i][j-1]!='B' and a[i][j-1]!='B':
                    a[i-1][j]='#'
                if j!=n-1 and a[i][j+1]!='B' and a[i][j+1]!='B':
                    a[i-1][j]='#'
    g=0
    for i in range (n):
        for j in range (m):
            if a[i][j]=='G':
                g+=1
                c=0
                if i!=0 and a[i-1][j]!='.':
                    c+=1
                elif i==0:
                    c+=1
                if i!=n-1 and a[i+1][j]!='.':
                    c+=1
                elif i==n-1:
                    c+=1
                if j!=0 and a[i][j-1]!='.':
                    c+=1
                elif j==0:
                    c+=1
                if j!=n-1 and a[i][j+1]!='.':
                    c+=1
                elif j==n-1:
                    c+=1
                if c==4:
                    ch=0
    if a[n-1][m-1]=='B':
        ch=0
    if a[n-1][m-1]=='#' and g!=0:
        ch=0
    if ch==1:
        print("YES")
    else:
        print("NO")