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 dfs(u,visited,good,d,n,m):
    visited[u]=True
    c=[0,False]
    if(u==n*m):
        c[1]=True

    if(good[u]=='G'):
        c[0]+=1
    for i in d[u]:
        if(visited[i]==False):
            dr=dfs(i,visited,good,d,n,m)
            c[0]+=dr[0]
            c[1]^=dr[1]
    return c

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


def main():
    for _ in range(int(input())):
        n,m=map(int,input().split())
        good=[0]*(n*m+1)
        ar=[]
        count=0
        for i in range(n):
            ar.append(list(input()))
        if (n * m == 1 and (ar[0][0]=='G' or ar[0][0]=='.')):
            print('YES')
            continue
        bl=True
        for i in range(n):
            for j in range(m):
                if(ar[i][j]=='G'):
                    if(j+1<m and ar[i][j+1]=='B'):
                        bl=False
                    if(j-1>=0 and ar[i][j-1]=='B'):
                        bl=False
                    if(i-1>=0 and ar[i-1][j]=='B'):
                        bl=False
                    if(i+1<n and ar[i+1][j]=='B'):
                        bl=False
                    if(bl==False):
                        break
            if(bl==False):
                break
        if(bl==False):
            print('No')
            continue
        for i in range(n):
            for j in range(m):
                if(ar[i][j]=='G'):
                    count+=1
                if (ar[i][j] == 'B'):
                    if (j + 1 < m and ar[i][j + 1] == '.'):
                        ar[i][j + 1]='#'
                    if (j - 1 >= 0 and ar[i][j - 1] == '.'):
                        ar[i][j - 1]='#'
                    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(ar[n-1][m-1]=='#' and count>0):
            print('No')
            continue
        d=defaultdict(list)
        ct=0
        for i in range(n):
            for j in range(m):
                ct+=1
                if (ar[i][j] == '.' or ar[i][j]=='G'):
                    if (j + 1 < m and (ar[i][j + 1] == '.' or ar[i][j + 1] == 'G')):
                        d[ct].append(ct+1)
                    if (j - 1 >= 0 and (ar[i][j - 1] == '.' or ar[i][j - 1] == 'G')):
                        d[ct].append(ct-1)
                    if (i - 1 >= 0 and (ar[i - 1][j] == '.' or ar[i - 1][j] == 'G')):
                        d[ct].append(ct-m)
                    if (i + 1 < n and (ar[i + 1][j] == '.' or ar[i + 1][j] == 'G')):
                        d[ct].append(ct+m)

                if(ar[i][j]=='G'):
                    good[ct]='G'

        if(len(d)==0):
            print('Yes')
            continue
        visited=[False]*(n*m+1)
        ans=False
        for i in range(1,n*m+1):
            if(i in d):
                val= dfs(i,visited,good,d,n,m)
                #print(val[0],val[1])
                if(val[0]==count and val[1]==True):
                    ans=True
                    break
        if(ans):
            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()
