for i in range(int(input())):
    n,m=map(int,input().split())
    l=[]
    for i in range(n):
        l.append(list(input()))
    f=0
    c1=0
    for i in range(n):
        for j in range(m):
            if l[i][j]=='B':
                if i-1>=0:
                    if l[i-1][j]=='G':
                        f=1
                        break
                    elif l[i-1][j]=='.':
                        l[i-1][j]='#'
                if i+1<n:
                    if l[i+1][j]=='G':
                        f=1
                        break
                    elif l[i+1][j]=='.':
                        l[i+1][j]='#'
                if j+1<m:
                    if l[i][j+1]=='G':
                        f=1
                        break
                    elif l[i][j+1]=='.':
                        l[i][j+1]='#'
                if j-1>=0:
                    if l[i][j-1]=='G':
                        f=1
                        break
                    elif l[i][j-1]=='.':
                        l[i][j-1]='#'
            elif l[i][j]=='G':
                c1+=1
        if f==1:
            print("No")
            break
    if f==0:
        c=0
        f=0
        s=set()
        q=[(n-1,m-1)]
        s.add((n-1,m-1))
        for cell in q:
            a,b=cell
            if l[a][b]=='#':
                continue
            elif l[a][b]=='G':
                c+=1
            elif l[a][b]=='B':
                f=1
            if a-1>=0:
                if (a-1,b) not in s:
                    s.add((a-1,b))
                    q.append((a-1,b))
            if a+1<n:
                if (a+1,b) not in s:
                    s.add((a+1,b))
                    q.append((a+1,b))
            if b+1<m:
                if (a,b+1) not in s:
                    s.add((a,b+1))
                    q.append((a,b+1))
            if b-1>=0:
                if (a,b-1) not in s:
                    s.add((a,b-1))
                    q.append((a,b-1))
        #print(list(s))
        if (f==1 or c!=c1):
            print("No")
        else:
            print("Yes")
