#!/usr/bin/env python
from __future__ import division, print_function

import os
import sys
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


class UnionFind:
    def __init__(self, n):
        self.parent = list(range(n))

    def find(self, a):
        acopy = a
        while a != self.parent[a]:
            a = self.parent[a]
        while acopy != a:
            self.parent[acopy], acopy = a, self.parent[acopy]
        return a

    def union(self, a, b):
        self.parent[self.find(b)] = self.find(a)


def main():
    t = int(input())

    for _ in range(t):
        n, m = map(int, input().split())
        maze = [list(input()) for _ in range(n)]

        good = []
        bad = []

        for i in range(n):
            for j in range(m):
                if maze[i][j] == 'G':
                    good.append(i * m + j)
                elif maze[i][j] == 'B':
                    bad.append(i * m + j)

                    if i != 0 and maze[i - 1][j] == '.':
                        maze[i - 1][j] = '#'
                    if j != 0 and maze[i][j - 1] == '.':
                        maze[i][j - 1] = '#'

                    if i != n - 1 and maze[i + 1][j] == '.':
                        maze[i + 1][j] = '#'
                    if j != m - 1 and maze[i][j + 1] == '.':
                        maze[i][j + 1] = '#'

        uf = UnionFind(n * m)
        for i in range(n):
            for j in range(m):
                if i != n - 1 and maze[i][j] != '#' and maze[i + 1][j] != '#':
                    uf.union(i * m + j, (i + 1) * m + j)
                if j != m - 1 and maze[i][j] != '#' and maze[i][j + 1] != '#':
                    uf.union(i * m + j, i * m + (j + 1))

                if i != 0 and maze[i][j] != '#' and maze[i - 1][j] != '#':
                    uf.union(i * m + j, (i - 1) * m + j)
                if j != 0 and maze[i][j] != '#' and maze[i][j - 1] != '#':
                    uf.union(i * m + j, i * m + (j - 1))


        exit_find = uf.find(n * m - 1)

        good_esc = all(uf.find(i) == exit_find for i in good)
        bad_esc = all(uf.find(i) == exit_find for i in bad) if bad else False

        print('Yes' if good_esc and (not bad_esc) else 'No')


# region fastio

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")

# endregion

if __name__ == "__main__":
    main()
