def yn(arr,n,m):
    for i in range(n):
        for j in range(m):
            if(arr[i][j]=="B"):
                if(j-1>=0 and arr[i][j-1]!="G" and arr[i][j-1]!="B" ):
                    arr[i][j-1]="#"
                if(j+1<m and arr[i][j+1]!="G" and arr[i][j+1]!="B" ):
                    arr[i][j+1]="#"
                if(i-1>=0 and arr[i-1][j]!="G" and arr[i-1][j]!="B" ):
                    arr[i-1][j]="#"
                if(i+1<n and arr[i+1][j]!="G" and arr[i+1][j]!="B" ):
                    arr[i+1][j]="#"
                if(j-1>=0 and arr[i][j-1]=="G"):
                    return "No"
                if(j+1<m and arr[i][j+1]=="G"):
                    return "No"
                if(i-1>=0 and arr[i-1][j]=="G"):
                    return "No"
                if(i+1<n and arr[i+1][j]=="G"):
                    return "No"
    return arr
for _ in range(int(input())):
    vis=[[False]*(62) for i in range(62)]
    n,m=map(int,input().split())
    arr=[]
    ng=0
    gc=0
    for i in range(n):
        s=input()
        l=[]
        for j in s:
            if(j=="G"):
                ng+=1
            l.append(j)
        arr.append(l)
    arr2=yn(arr,n,m)
    if arr2=="No":
        print("No")
    else:
        tags = [[False] * m for _ in range(n)]
        todo = [(n-1, m-1)]
        while len(todo) > 0:
            newtodo = []
            for a, b in todo:
                if tags[a][b] or arr2[a][b] == "#":
                    continue
                tags[a][b] = True
                if a > 0:
                    newtodo.append((a-1, b))
                if b > 0:
                    newtodo.append((a, b-1))
                if a < n - 1:
                    newtodo.append((a+1, b))
                if b < m - 1:
                    newtodo.append((a, b+1))
            todo = newtodo
        for i in range(n):
            for j in range(m):
                if tags[i][j]==True and arr2[i][j]=="G":
                    gc+=1
        if(ng==gc):
            print("Yes")
        else:
            print("No")
    

    
    
            