import os
import sys
from io import BytesIO, IOBase



def main():
    di = (-1, 1, 0, 0)
    dj = (0, 0, -1, 1)

    def dfs(maze, i, j, visited, n, m):
        if maze[i][j] != '#':
            visited[i][j] = True
        else:
            return
        for d in range(4):
            ni = i + di[d]
            nj = j + dj[d]
            if (ni >= 0) and (nj >= 0) and (ni < n) and (nj < m) and (not visited[ni][nj]):
                dfs(maze, ni, nj, visited, n, m)
        return

    cases = int(input())
    for t in range(cases):
        n, m = r_array()
        maze = [list(input()) for i in range(n)]
        gcount = 0
        f = 0

        for i in range(n):
            for j in range(m):
                if maze[i][j] == 'B':
                    if j < m - 1:
                        if maze[i][j + 1] == 'G':
                            f = 1
                            break
                        elif maze[i][j + 1] == '.':
                            maze[i][j + 1] = '#'

                    if j > 0:
                        if maze[i][j - 1] == 'G':
                            f = 1
                            break
                        elif maze[i][j - 1] == '.':
                            maze[i][j - 1] = '#'

                    if i < n - 1:
                        if maze[i + 1][j] == 'G':
                            f = 1
                            break
                        elif maze[i + 1][j] == '.':
                            maze[i + 1][j] = '#'

                    if i > 0:
                        if maze[i - 1][j] == 'G':
                            f = 1
                            break
                        elif maze[i - 1][j] == '.':
                            maze[i - 1][j] = '#'
                elif maze[i][j] == 'G':
                    gcount += 1
            if f == 1:
                break

        if maze[-1][-1] == '#':
            if gcount == 0:
                write('Yes')
            else:
                write('No')
            continue

        if f == 1:
            write('No')
            continue

        visited = [[False for j in range(m)] for i in range(n)]

        # print('do dfs gcount :',gcount)
        # print('here')
        dfs(maze, n - 1, m - 1, visited, n, m)
        # print(gc)
        # print(visited)
        # print(maze)
        f = 0
        for i in range(n):
            for j in range(m):
                if maze[i][j] == 'G' and not visited[i][j]:
                    f = 1
                    break
            if f == 1:
                break
        if f == 1:
            write('No')
        else:
            write("Yes")


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)


def input():
    return sys.stdin.readline().rstrip("\r\n")


def write(*args, end='\n'):
    for x in args:
        sys.stdout.write(str(x) + ' ')
    sys.stdout.write(end)


def r_array():
    return [int(x) for x in input().split()]


def r_int():
    return int(input())


def w_array(arr):
    for x in arr:
        write(x, end=' ')
    write()


if __name__ == "__main__":
    main()
