"""

"""

import sys
from sys import stdin

TT = int(stdin.readline())

def solve(c,want):

    n = len(c)
    m = len(c[0])

    c_copy = [[ c[i][j] for j in range(m) ] for i in range(n)]
    c = c_copy

    ans = []

    # 右上
    for imj in range(-(m-1),0):
        x,y = 0,0
        route = []

        c[x][y] ^= 1
        while x-y != imj+1:
            route.append( "R" )
            y += 1
            c[x][y] ^= 1

        while x != n-1 and y != m-1:
            if c[x][y+1] != want:
                route.append("R")
                y += 1
                c[x][y] ^= 1
                route.append("D")
                x += 1
                c[x][y] ^= 1
            else:
                route.append("D")
                x += 1
                c[x][y] ^= 1
                route.append("R")
                y += 1
                c[x][y] ^= 1

        while x != n-1:
            route.append("D")
            x += 1
            c[x][y] ^= 1

        while y != m-1:
            route.append("R")
            y += 1
            c[x][y] ^= 1

        ans.append(route)

    # 左下
    for imj in range(n-1,0,-1):
        x,y = 0,0
        route = []

        c[x][y] ^= 1
        while x-y != imj-1:
            route.append( "D" )
            x += 1
            c[x][y] ^= 1

        while x != n-1 and y != m-1:
            if c[x+1][y] != want:
                route.append("D")
                x += 1
                c[x][y] ^= 1
                route.append("R")
                y += 1
                c[x][y] ^= 1
            else:
                route.append("R")
                y += 1
                c[x][y] ^= 1
                route.append("D")
                x += 1
                c[x][y] ^= 1

        while x != n-1:
            route.append("D")
            x += 1
            c[x][y] ^= 1

        while y != m-1:
            route.append("R")
            y += 1
            c[x][y] ^= 1

        ans.append(route)

    flag = True
    for i in range(n):
        for j in range(m):
            if c[0][0] != c[i][j]:
                flag = False

    # print (c,ans)
    if flag:
        return ans
    else:
        return None

for loop in range(TT):

    n,m = map(int,stdin.readline().split())

    c = [list(stdin.readline()[:-1]) for i in range(n)]

    for i in range(n):
        for j in range(m):
            if c[i][j] == "B":
                c[i][j] = 1
            else:
                c[i][j] = 0

    
    ans1 = solve(c,0)
    if ans1 != None:
        print ("YES")
        print (len(ans1))
        for cs in ans1:
            print ("".join(cs))
        continue

    ans2 = solve(c,1)
    if ans2 != None:
        print ("YES")
        print (len(ans2))
        for cs in ans2:
            print ("".join(cs))
        continue

    print ("NO")