import sys


def input():
    return sys.stdin.readline().rstrip()


dxy = ((-1, 0), (0, -1), (1, 0), (0, 1))


class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * (n)

    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        if self.parents[x] > self.parents[y]:
            x, y = y, x
        self.parents[x] += self.parents[y]
        self.parents[y] = x

    def size(self, x):
        return -self.parents[self.find(x)]

    def same(self, x, y):
        return self.find(x) == self.find(y)

    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n + 1) if self.find(i) == root]

    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]

    def group_count(self):
        return len(self.roots())

    def all_group_members(self):
        return {r: self.members(r) for r in self.roots()}


def slv():
    #print("hello world")
    n, m = map(int, input().split())
    S = [list(input()) for i in range(n)]
    for i in range(n):
        for j in range(m):
            if S[i][j] == 'G':
                for di, dj in dxy:
                    if 0 <= i + di < n and 0 <= j + dj < m and S[i + di][j + dj] == "B":
                        print("No")
                        return

            elif S[i][j] == "B":
                for di, dj in dxy:
                    if 0 <= i + di < n and 0 <= j + dj < m and S[i + di][j + dj] == ".":
                        S[i + di][j + dj] = "#"

    dsu = UnionFind(n*m)
    for i in range(n):
        for j in range(m):
            if S[i][j] == "#":
                continue
            p = m * i + j
            for di, dj in dxy:
                i_1, j_1 = i + di, j + dj
                if 0 <= i_1 < n and 0 <= j_1 < m and S[i_1][j_1] != "#":
                    q = m * i_1 + j_1
                    dsu.union(p, q)
    for i in range(n):
        for j in range(m):
            if S[i][j] == "B":
                p = m * i + j
                q = m * n - 1
                if dsu.same(p, q) == True:
                    print("No")
                    return
            elif S[i][j] == "G":
                p = m * i + j
                q = m * n - 1
                if dsu.same(p, q) == False:
                    print("No")
                    return
    print("Yes")
    return


def main():
    t = int(input())
    for _ in range(t):
        slv()
    return


if __name__ == "__main__":
    # in_txt = open("in.txt", "r")
    # out_txt = open("out.txt", "w")
    # sys.stdin = in_txt
    # sys.stdout = out_txt
    main()
