from __future__ import division, print_function
 
import os
import sys, math
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


def main():
    Test = int(input())
    while Test:
        Test -= 1
        n, m = map(int, input().split())
        mat = []
        vis = []
        for i in range(n):
            tmp = list(input())
            vis.append([False]*m)
            mat.append(tmp)
        ans = True
        dirs = [[1, 0], [-1, 0], [0, 1], [0, -1]]
        def check(i, j):
            return i>=0 and j>=0 and i < n and j < m
        for i in range(n):
            for j in range(m):
                if mat[i][j] == 'B':
                    for di in dirs:
                        x = i + di[0]
                        y = j + di[1]
                        if check(x, y) and mat[x][y] == '.':
                            mat[x][y] = '#'
        q = list()
        if mat[n-1][m-1] == '.':
            q.append((n-1, m-1))
            vis[n-1][m-1] = True
        while len(q):
            p = q.pop(0)
            for di in dirs:
                x = p[0] + di[0]
                y = p[1] + di[1]
                if check(x, y) and not vis[x][y] and mat[x][y] != '#':
                    q.append((x, y))
                    vis[x][y] = True
        for i in range(n):
            for j in range(m):
                if mat[i][j] == 'G' and not vis[i][j]:
                    ans = False
                elif mat[i][j] == 'B' and vis[i][j]:
                    ans = False
        print ('yes' if ans else 'no')
    return None

# 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()