def check(ls,a,b,n,m):
    if a>=0 and a<n and b>=0 and b<m:
        if ls[a][b]!=-1:
            return True
    return False

def dfs(ls,i,j,n,m):
    ls1 = [(i,j)]
    st = set(ls1)
    z1 = [[0 for i in range(m)] for j in range(n)]
    z1[i][j] = 1
    x = [-1,0,1,0]
    y = [0,1,0,-1]
    ans = "NO"
    while len(st)!=0:
        (p,q) = st.pop()
        for k in range(4):
            a = p+x[k]
            b = q+y[k]
            # print(a,b)
            # print()
            if check(ls,a,b,n,m) and z1[a][b]==0:
                    st.add((a,b))
                    z1[a][b] = 1
    return z1
    
    



for lo in range(int(input())):
    n,m = map(int,input().split())
    ls = [[0 for i in range(m)] for j in range(n)]
    c = 0
    for i in range(n):
        st = input()
        for j in range(m):
            ls[i][j] = st[j]
            if st[j]=='G':
                c+=1
    if c==0:
        print("YES")
        continue
    
    ans = "YES"
    for i in range(n):
        for j in range(m):
            if ls[i][j]=='#':
                ls[i][j]=-1
            if ls[i][j]=='B':
                if (j-1)>=0:
                    if ls[i][j-1]=='G':
                        ans = "NO"
                    if ls[i][j-1]!='B':
                        ls[i][j-1]=-1
                if (i-1)>=0:
                    if ls[i-1][j]=='G':
                        ans = "NO"
                    if ls[i-1][j]!='B':
                        ls[i-1][j]=-1
                if (i+1)<n:
                    if ls[i+1][j]=='G':
                        ans = "NO"
                    if ls[i+1][j]!='B':
                        ls[i+1][j]=-1
                if (j+1)<m:
                    if ls[i][j+1]=='G':
                        ans = "NO"
                    if ls[i][j+1]!='B':
                        ls[i][j+1]=-1
                ls[i][j]=-1
    
    if ans=='NO' or ls[n-1][m-1]==-1:
        print('NO')
        continue
    ans = 'YES'
    #print(ls)
    ans1 = dfs(ls,n-1,m-1,n,m)
    for i in range(n):
        for j in range(m):
            if ls[i][j]=='G' and ans1[i][j]==0:
                ans = "NO"
                break
        if ans=="NO":
            break
    print(ans)  
