from __future__ import division, print_function

''' Hey stalker :) '''
INF = 10 ** 10
TEST_CASES = True
from collections import defaultdict

def main():
    n, m = get_list()
    mat = [list(input()) for _ in range(n)]
    def mark_border(a, b):
        if -1 < a < n and -1 < b < m:
            if mat[a][b] == "G":
                print("No")
                return True
            mat[a][b]="#" if mat[a][b]!="B" else "B"
        return False
    for i in range(n):
        for j in range(m):
            if mat[i][j]=="B":
                if mark_border(i-1,j) or mark_border(i+1,j) or mark_border(i, j+1) or mark_border(i, j-1): return
    #[print(li) for li in mat]
    reachable = [[0]*m for _ in range(n)]
    que = [(n-1, m-1)] if mat[n-1][m-1]!="#" else []
    def update_que(a,b):
        if -1 < a < n and -1 < b < m and (mat[a][b]=="G" or mat[a][b]==".") and reachable[a][b]==0:
            reachable[a][b]=1
            new_q.append((a,b))
    while len(que)>0:
        new_q = []
        for i,j in que:
            reachable[i][j] = 1
            update_que(i-1,j)
            update_que(i+1,j)
            update_que(i,j-1)
            update_que(i,j+1)
        que = new_q
    for i in range(n):
        for j in range(m):
            if mat[i][j]=="G" and reachable[i][j]==0:
                print("No")
                return
    print("Yes")





''' FastIO Footer: PyRival Library, Thanks @c1729 and contributors '''
import os
import sys
#from bisect import bisect_left, bisect_right
from io import BytesIO, IOBase

if sys.version_info[0] < 3:
    from __builtin__ import xrange as range
    from future_builtins import ascii, filter, hex, map, oct, zip
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")


def print(*args, **kwargs):
    """Prints the values to a stream, or to sys.stdout by default."""
    sep, file = kwargs.pop("sep", " "), kwargs.pop("file", sys.stdout)
    at_start = True
    for x in args:
        if not at_start:
            file.write(sep)
        file.write(str(x))
        at_start = False
    file.write(kwargs.pop("end", "\n"))
    if kwargs.pop("flush", False):
        file.flush()


if sys.version_info[0] < 3:
    sys.stdin, sys.stdout = FastIO(sys.stdin), FastIO(sys.stdout)
# else:
#     sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)

input = lambda: sys.stdin.readline().rstrip("\r\n")
get_int = lambda: int(input())
get_list = lambda: list(map(int, input().split()))

if __name__ == "__main__":
    if TEST_CASES:
        [main() for _ in range(int(input()))]
    else:
        main()
