import os
import sys
from io import BytesIO, IOBase
 
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")
#######################################
import sys
sys.setrecursionlimit(2500)
def dfs(x):
    v[x]=1
    for i in adj[x]:
        if not v[i]:
            dfs(i)
t=int(input())
for i in range(t):
    n,m=map(int,input().split())
    l=[]
    for j in range(n):
        l.append(list(input()))
    g,b=0,0
    ans=True
    adj=[[] for j in range(n*m+1)]
    v=[0]*(n*m+1)
    l2=[]
    for j in range(n):
        for k in range(m):
            if l[j][k]=='B':
                b+=1
                l2.append(j*m+k+1)
                if k!=m-1:
                    if l[j][k+1]=='.':
                        l[j][k+1]='#'
                    if l[j][k+1]=='G':
                        adj[j*m+k+1].append(j*m+k+2)
                        adj[j*m+k+2].append(j*m+k+1)
                if k!=0:
                    if l[j][k-1]=='.':
                        l[j][k-1]='#'
                    if l[j][k-1]=='G':
                        adj[j*m+k+1].append(j*m+k)
                        adj[j*m+k].append(j*m+k+1)
                if j!=0:
                    if l[j-1][k]=='.':
                        l[j-1][k]='#'
                    if l[j-1][k]=='G':
                        adj[j*m+k+1].append((j-1)*m+k+1)
                        adj[(j-1)*m+k+1].append(j*m+k+1)
                if j!=n-1:
                    if l[j+1][k]=='.':
                        l[j+1][k]='#'
                    if l[j+1][k]=='G':
                        adj[j*m+k+1].append((j+1)*m+k+1)
                        adj[(j+1)*m+k+1].append(j*m+k+1)
            if l[j][k]=='G':
                g+=1
    if g==0:
        print("Yes")
    else:
        l1=[]
        for j in range(n):
            for k in range(m):
                if l[j][k]=='.' or l[j][k]=='G':
                    if l[j][k]=='G':
                        l1.append(j*m+k+1)
                    if k!=m-1:
                        if l[j][k+1]=='.' or l[j][k+1]=='G':
                            adj[j*m+k+1].append(j*m+k+2)
                            adj[j*m+k+2].append(j*m+k+1)
                    if j!=n-1:
                        if l[j+1][k]=='.' or l[j+1][k]=='G':
                            adj[j*m+k+1].append((j+1)*m+k+1)
                            adj[(j+1)*m+k+1].append(j*m+k+1)
        dfs(l1[0])
        for j in l1:
            if v[j]==0:
                ans=False
                break
        if v[n*m]==0:
            ans=False
        for j in l2:
            if v[j]==1:
                ans=False
                break
        if ans:
            print("Yes")
        else:
            print("No")

    
    
