#include <bits/stdc++.h>
using namespace std;
namespace Slongod{
const int N = 5e4+7 , inf = 0x3f3f3f3f;
namespace wll
{
	int econt , s , t , head[N] , hu[N] , dep[N];
	struct EDGE{int to , nxt , w;}edge[N*10];
	inline void _add(int x , int y , int w){edge[++econt].to = y; edge[econt].nxt = head[x]; head[x] = econt; edge[econt].w = w;}
	inline void add(int x , int y , int w){_add(x , y , w); _add(y , x , 0);}
	inline bool bfs()
	{
		for (int i = s; i <= t; i++){dep[i] = -1; hu[i] = head[i];}
		queue <int> q; q.push(s); dep[s] = 0;
		while(!q.empty()) {
			int u = q.front(); q.pop();
			for (int i = head[u]; i; i = edge[i].nxt) {
				int v = edge[i].to , w = edge[i].w;
				if (w and dep[v] == -1) {
					dep[v] = dep[u] + 1; q.push(v);
				}
			}
		} return dep[t] != -1;
	}
	int dfs(int u , int f)
	{
		if (u == t){return f;} int used = 0;
		for (int &i = hu[u]; i; i = edge[i].nxt) {
			int v = edge[i].to , w = edge[i].w;
			if (dep[v] == dep[u] + 1 and w) {
				int tmp = dfs(v , min(f-used , w));
				edge[i].w -= tmp; edge[i^1].w += tmp; used += tmp;
			}
		} if (!used){dep[u] = -1;} return used;
	}
	inline int dinic(){int re = 0; while(bfs()){re += dfs(s , inf);} return re;}
	inline void init(int S , int T){s = S; t = T; for (int i = S; i <= T; i++){head[i] = 0;} econt = 1;}
}
int n , m , s , t , ans;
inline int id(int x , int y){return (x - 1) * m + y;}
inline int rid(int x , int y , int op){return id(n , m) + id(x , y) + op * id(n - 1 , m - 1);}
void main()
{
	int T; cin >> T;
	while(T--) {
		cin >> n >> m; s = 0; t = id(n , m) * 3 + 1; ans = 0; wll::init(s , t);
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= m; j++) {
				char a; cin >> a;
				if ((i+j)&1) {
					if (a == 'W'){wll::add(s , id(i,j) , inf); wll::add(id(i,j) , t , 1);}
					if (a == 'B'){wll::add(id(i,j) , t , inf); wll::add(s , id(i,j) , 1);}
					if (a == '?'){wll::add(s , id(i,j) , 1); wll::add(id(i,j) , t , 1);}
				} else {
					if (a == 'W'){wll::add(id(i,j) , t , inf); wll::add(s , id(i,j) , 1);}
					if (a == 'B'){wll::add(s , id(i,j) , inf); wll::add(id(i,j) , t , 1);}
					if (a == '?'){wll::add(s , id(i,j) , 1); wll::add(id(i,j) , t , 1);}
				}
				if (i + 1 <= n and j + 1 <= m) { ans++;
					wll::add(rid(i,j,0) , rid(i,j,1) , 1);
					
					wll::add(id(i,j) , rid(i,j,0) , inf);
					wll::add(rid(i,j,1) , id(i,j) , inf);
					
					wll::add(id(i,j+1) , rid(i,j,0) , inf);
					wll::add(rid(i,j,1) , id(i,j+1) , inf);
					
					wll::add(id(i+1,j) , rid(i,j,0) , inf);
					wll::add(rid(i,j,1) , id(i+1,j) , inf);
					
					wll::add(id(i+1,j+1) , rid(i,j,0) , inf);
					wll::add(rid(i,j,1) , id(i+1,j+1) , inf);
				}
			}
		} cout << ans - wll::dinic() + n * m << '\n';
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= m; j++) {
				if ((i+j)&1) {
					cout << (wll::dep[id(i,j)] != -1 ? 'W' : 'B');
				} else {
					cout << (wll::dep[id(i,j)] != -1 ? 'B' : 'W');
				}
			} cout << '\n';
		}
	}
}
}int main()
{
	ios :: sync_with_stdio(0);
	cin.tie(0) , cout.tie(0);
	return Slongod :: main(),0;
}