import os
import heapq
import sys
import math
import operator
from collections import defaultdict
from io import BytesIO, IOBase

"""def gcd(a,b):
    if b==0:
        return a
    else:
        return gcd(b,a%b)"""

"""def pw(a,b):
    result=1
    while(b>0):
        if(b%2==1): result*=a
        a*=a
        b//=2
    return result"""


def inar():
    return [int(k) for k in input().split()]


def main():
    for _ in range(int(input())):
        n, m = map(int, input().split())
        ar = []
        for i in range(n):
            ar.append(list(input()))

        for i in range(n):
            for j in range(m):
                if(ar[i][j]=='B'):
                    if(i-1>=0 and ar[i-1][j]=='.'):
                        ar[i-1][j]='#'
                    if (i + 1 < n and ar[i + 1][j] == '.'):
                        ar[i + 1][j] = '#'
                    if (j - 1 >= 0 and ar[i][j-1] == '.'):
                        ar[i][j-1] = '#'
                    if (j + 1 <m and ar[i][j+1] == '.'):
                        ar[i][j+1] = '#'
        q=[]
        visited=[]
        for i in range(n):
            visited.append([False]*m)

        if(ar[n-1][m-1]=='.'):
            q.append((n-1,m-1))
            visited[n-1][m-1]=True
        # visited[n-1][m-1]=False
        while(q):
            pos=q.pop()
            i=pos[0]
            j=pos[1]
            if (i - 1 >= 0 and ar[i - 1][j] != '#' and visited[i-1][j]==False):
                q.append((i-1,j))
                visited[i-1][j]=True
            if (i + 1 < n and ar[i + 1][j] != '#' and visited[i+1][j]==False):
                q.append((i+1,j))
                visited[i + 1][j] = True
            if (j - 1 >= 0 and ar[i][j-1] != '#' and visited[i][j-1]==False):
                q.append((i,j-1))
                visited[i][j - 1] = True
            if (j + 1 < m and ar[i][j+1] != '#' and visited[i][j+1]==False):
                q.append((i,j+1))
                visited[i][j+1] = True
        good=True
        for i in range(n):
            for j in range(m):
                if((ar[i][j]=='G' and visited[i][j]==False) or (ar[i][j]=='B' and visited[i][j]==True)):
                    good=False
                    break
        if(good):
            print('Yes')
        else:
            print('No')

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")

if __name__ == "__main__":
    main()