import itertools as it
import sys
sys.setrecursionlimit(10**5) 
l=[[0,1],[1,0],[-1,0],[0,-1]]
c=0
def dfs(i,j,d,visited,m,n):
    global c,l
    if(d[i][j]=='G'):
        c+=1
    if(d[i][j]!='#'):
        for k in l:
            if(n>i+k[0]>-1 and m>j+k[1]>-1 and ((i+k[0],j+k[1]) not in visited) and d[i+k[0]][j+k[1]]!='#'):
                visited.add((i+k[0],j+k[1]))
                dfs(i+k[0],j+k[1],d,visited,m,n)

def main():
    global c
    
    for _ in range(int(input())):
        try:
            c=0
            n,m=map(int,input().split())
            l=[list(input()) for i in range(n)]
            alpha=list(it.chain.from_iterable(l))
            # print(alpha)
            b,f,g=[],0,0
            m1=-1
            for i in range(n):
                for j in range(m):
                    if(l[i][j]=='G'):
                        m1=(i,j)
                        break
            for i in range(n):
                for j in range(m):
                    if(l[i][j]=='B'):
                        b.append((i,j))
                        if(i-1>=0 and l[i-1][j]=='G'):
                            f=1
                        if(i+1<=n-1 and l[i+1][j]=='G'):
                            f=1
                        if(j-1>=0 and l[i][j-1]=='G'):
                            f=1
                        if(j+1<=m-1 and l[i][j+1]=='G'):
                            f=1
                        if(i-1>=0 and l[i-1][j]=='.'):
                            l[i-1][j]='#'
                        if(i+1<=n-1 and l[i+1][j]=='.'):
                            l[i+1][j]='#'
                        if(j-1>=0 and l[i][j-1]=='.'):
                            l[i][j-1]='#'
                        if(j+1<=m-1 and l[i][j+1]=='.'):
                            l[i][j+1]='#'
            
            if(m1!=-1):
                dfs(n-1,m-1,l,set(),m,n)
                # print(m1,l,c,f,alpha.count('G'))
                if(l[-1][-1]=='#'):
                    f=1
            else:
                f=0
            if(f!=1 and alpha.count('G')==c):
                print("Yes")
                pass
            else:
                print('no')
        except  Exception as e:
            print(e)
main()