t = int(input())
S = [1,-1,0,0]
D = [0,0,1,-1]

def good(r,c,n,m):
    return r>= 0 and c>=0 and r<n and c<m

def f(matrix, n, m):
    posizioni = list()
    for row in range(n):
        for col in range(m):
            if matrix[row][col] == "G":
                posizioni.append((row, col))
    
    
    visited = set()
    for row in range(n):
        for col in range(m):
            if (row, col) not in visited and matrix[row][col] == "B":
                stack = [[row, col]]
                while stack:
                    r, c = stack.pop()
                    visited.add((r,c))
                    for i in range(4):
                        R = r + S[i]
                        C = c + D[i]
                        if good(R, C, n, m) and (R, C) not in visited:
                            visited.add((R,C))
                            if matrix[R][C] == "B":
                                stack.append([R,C])
                                matrix[R][C] = "#"
                            elif matrix[R][C] == "G":
                                return "No"
                            else:
                                matrix[R][C] = "#"
    
    if matrix[n-1][m-1] == "#":
        return "No"
    
    ok = [[0 for _ in range(m)] for _ in range(n)]
    visited2 = set()
    
    stack = [[n-1, m-1]]
    while stack:
        r, c = stack.pop()
        visited2.add((r,c))
        ok[r][c] = 1
        for i in range(4):
            R = r + S[i]
            C = c + D[i]
            if good(R, C, n, m) and (R, C) not in visited2:
                visited2.add((R,C))
                if matrix[R][C] in [".", "G"]:
                    stack.append([R,C])
    
    for pos in posizioni:
        if ok[pos[0]][pos[1]] == 0:
            return "No"
            
    return "Yes"

for test in range(t):
    [n,m] = list(map(int, input().rstrip().split()))
    matrix = [["." for _ in range(m)] for _ in range(n)]
    countG = 0
    for row in range(n):
        s = input()
        for col in range(m):
            matrix[row][col] = s[col]
            if matrix[row][col] == "G":
                countG += 1
    if countG == 0:
        print("Yes")
    else:
        print(f(matrix, n, m))
    
