import sys

input = sys.stdin.readline


for i in range(int(input())):
    n, m = map(int, input().split())
    a = [['.'] * (m + 1) for _ in range(n+1)]
    ans = True

    g = list()


    for i in range(n):
        line = input().strip()
        for j, c in enumerate(line):
            if c == 'B':
                a[i][j] = 'B'
                if a[i - 1][j] == 'G':
                    ans = False
                a[i - 1][j] = '#'

                if a[i + 1][j] == 'G':
                    ans = False
                a[i + 1][j] = '#'

                if a[i][j + 1] == 'G':
                    ans = False
                a[i][j + 1] = '#'

                if a[i][j - 1] == 'G':
                    ans = False
                a[i][j - 1] = '#'

            if c == 'G':
                if a[i][j] == '#':
                    ans = False
                a[i][j] = 'G'
                g.append((i,j))

            if c == '#':
                a[i][j] = '#'

    if ans is False:
        print('No')
        continue

    a.pop()
    for l in a:
        l.pop()

    front = [(n-1, m-1)]
    visited = {(n-1, m-1)}
    while front:
        new_front = []
        for p in front:
            i = a[p[0]][p[1]]


            if i == '.' or i == 'G':
                if i == 'G':
                    g.remove(p)
                for x, y in ((0, 1), (0, -1), (-1, 0), (1, 0)):
                    if p[0]+x == n:
                        continue
                    if p[1]+y == m:
                        continue
                    if p[0]+x == -1:
                        continue
                    if p[1]+y == -1:
                        continue

                    ni = (p[0]+x, p[1]+y)
                    if ni not in visited:
                        new_front.append(ni)
                        visited.add(ni)
        front = new_front[:]

    if g:
        print('No')
    else:
        print('Yes')

'''
1
5 5
.....
.G...
.B..B
.....
.B...
'''


# for i in range(int(input())):
#     n, m = map(int, input().split())
#     l = list()
#     l_block = set()
#     ans = True
#
#     for i in range(n):
#         line = input().strip()
#         s = []
#
#
#
#         n = False
#
#         for j, c in enumerate(line.strip()):
#             s.append(c)
#             if c == 'B':
#                 if j:
#                     if s[j - 1] == 'G':
#                         ans = False
#                     s[j - 1] = '#'
#                 if i:
#                     if l[i-1][j] == 'G':
#                         ans = False
#                     l[i-1][j] = '#'
#                 n = True
#                 l_block.add(j)
#
#             elif n == True:
#                 if s[j] == 'G':
#                     ans = False
#                 s[j] = '#'
#
#         for c in l_block:
#             if s[c] == 'G':
#                 ans = False
#             s[c] = '#'
#
#         l_block = set()
#         l.append(s)
#
#     for li in l:
#         print(li)
#



# for _ in range(int(input())):
#     n = int(input())
#     a = map(int, input().split())
#     b = map(int, input().split())
#
#
#
#     if True:
#         print('Yes')
#     else:
#         print('No')
#

'''
5
4
10 20 20 30
0 1 0 1
3
3 1 2
0 1 1
4
2 2 4 8
1 1 1 1
3
5 15 4
0 0 0
4
20 10 100 50
1 0 0 1


'''