"""
NTC here
"""
 
 
#!/usr/bin/env python
import os
import sys
from io import BytesIO, IOBase

profile = 0
pypy = 1
 
 
def iin(): return int(input())


def lin(): return list(map(int, input().split()))


class Disjoint_set:
    class node:
        def __init__(self, a):
            self.value = a
            self.p = self
            self.rank = 0

    def __init__(self, a):
        self.data = {i: self.make_set(i) for i in a}

    def make_set(self, val):
        return self.node(val)

    def union(self, x, y):
        # print('UNION: ', x, y)
        self.link(self.find_set(self.data[x]), self.find_set(self.data[y]))

    def link(self, val1, val2):
        if val1.rank > val2.rank:
            val2.p = val1
            val1.rank += 1
        else:
            val1.p = val2
            val2.rank += 1

    def find_set(self, val):
        if val.p.value != val.value:
            val.p = self.find_set(val.p)
        return val.p
        
    def find_parent(self, val):
        return self.find_set(self.data[val]).value
 
def main():
    T = iin()
    dc = {'.':0, '#':1, 'G':2, 'B':3}
    while T:
        T-=1
        n, m = lin()
        a = [[dc[j] for j in input()] for i in range(n)]
        # print(a)
        for i in range(n):
            for j in range(m):
                if a[i][j] == 3:
                    if i>0 and a[i-1][j] == 0:
                        a[i-1][j] = 1
                    if j>0 and a[i][j-1] == 0:
                        a[i][j-1] = 1
                    if i<n-1 and a[i+1][j] == 0:
                        a[i+1][j] = 1
                    if j<m-1 and a[i][j+1] == 0:
                        a[i][j+1] = 1
        # print(a)
        # find path
        arr = []
        for i in range(n):
            for j in range(m):
                arr.append((i, j))
        ds = Disjoint_set(arr)
        for i in range(n):
            for j in range(m):
                if a[i][j] == 1:continue
                if i>0 and a[i-1][j] != 1:
                    ds.union((i, j), (i-1, j))
                if j>0 and a[i][j-1] != 1:
                    ds.union((i, j), (i, j-1))
                if i<n-1 and a[i+1][j] != 1:
                    ds.union((i, j), (i+1, j))
                if j<m-1 and a[i][j+1] != 1:
                    ds.union((i, j), (i, j+1))
        parent = ds.find_parent((n-1, m-1))
        # print(parent)
        # check
        ans = True
        for i in range(n):
            for j in range(m):
                # print(ds.find_parent((i, j)))
                if a[i][j] == 2:
                    if ds.find_parent((i, j)) != parent:
                        ans = False
                elif a[i][j] == 3:
                    if ds.find_parent((i, j)) == parent:
                        ans = False
        # print(dp)
        print('Yes' if ans 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")
 
if pypy:
    sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
    input = lambda: sys.stdin.readline().rstrip("\r\n")
 
# endregion
 
if __name__ == "__main__":
    if profile:
        import cProfile
        cProfile.run('main()')
    else:
        main()