#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 = 0; i <= max(s,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 (f == used){break;}
			}
		} 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 , flag[N] , output[105][105];
const int dx[4] = {-1 , -1 , 0 , 0};
const int dy[4] = {-1 , 0 , -1 , 0};
#define id(x , y) ((x - 1) * (m - 1) + y)
#define rid(x , y , opt) (id(x , y) * 2 - opt)
inline bool cmp(int x , int y){return 1 <= x and x < n and 1 <= y and y < m;}
void main()
{
	int T; cin >> T;
	while(T--) {
		cin >> n >> m; ans = (n - 1) * (m - 1) * 2;
		s = 0; t = rid(n-1 , m-1 , 0) + 1;
		wll::init(s , t);
		for (int i = 1; i <= id(n-1,m-1); i++){flag[i] = 0;}
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= m; j++) {
				char a; cin >> a;
				if (((i + j) & 1) and a == 'W'){a = 'B';}
				else if (((i + j) & 1) and a == 'B'){a = 'W';}
				if (a != '?'){output[i][j] = (a == 'W' ? 1 : 2);}
				else{output[i][j] = 0;}
				for (int k = 0; k < 4; k++) {
					int tx = i + dx[k] , ty = j + dy[k];
					if (!cmp(tx , ty)){continue;}
					if (a == 'W'){flag[id(tx,ty)] |= 1;}
					if (a == 'B'){flag[id(tx,ty)] |= 2;}
				}
			}
		}
		for (int i = 1; i < n; i++) {
			for (int j = 1; j < m; j++) {
				wll::add(rid(i,j,1) , rid(i,j,0) , inf);
				if (flag[id(i,j)] == 0) {
					wll::add(s , rid(i,j,1) , 1);
					wll::add(rid(i,j,0) , t , 1);
				} else if (flag[id(i,j)] == 1) {
					ans--;
					wll::add(s , rid(i,j,1) , 1);
				} else if (flag[id(i,j)] == 2) {
					ans--;
					wll::add(rid(i,j,0) , t , inf);
				} else {
					ans -= 2;
				}
			}
		}
		for (int i = 1; i < n; i++) {
			for (int j = 1; j < m; j++) {
				if (flag[id(i,j)] == 3){continue;}
				if (i > 1) {
					for (int k = j; k <= j+1 and k < m; k++) {
						if (flag[id(i-1,k)] == 3){continue;}
						wll::add(rid(i,j,1) , rid(i-1,k,0) , inf);
						wll::add(rid(i-1,k,1) , rid(i,j,0) , inf);
					}
				}
				if (j > 1) {
					for (int k = i; k <= i+1 and k < n; k++) {
						if (flag[id(k,j-1)] == 3){continue;}
						wll::add(rid(i,j,1) , rid(k,j-1,0) , inf);
						wll::add(rid(k,j-1,1) , rid(i,j,0) , inf);
					}
				}
				if (i > 1 and j > 1 and flag[id(i-1,j-1)] != 3) {
					wll::add(rid(i,j,1) , rid(i-1,j-1,0) , inf);
					wll::add(rid(i-1,j-1,1) , rid(i,j,0) , inf);
				}
			}
		}
		cout << ans - wll::dinic() << '\n';
		for (int i = 1; i < n; i++) {
			for (int j = 1; j < m; j++) {
				if (wll::dep[rid(i,j,1)] != -1 and !(flag[id(i,j)]&2)) {
					for (int tx = i; tx <= i+1; tx++) {
						for (int ty = j; ty <= j+1; ty++) {
							output[tx][ty] = 1;
						}
					}
				}
			}
		}
		for (int i = 1; i < n; i++) {
			for (int j = 1; j < m; j++) {
				if (wll::dep[rid(i,j,1)] == -1 and !(flag[id(i,j)]&1)) {
					for (int tx = i; tx <= i+1; tx++) {
						for (int ty = j; ty <= j+1; ty++) {
							output[tx][ty] = 2;
						}
					}
				}
			}
		}
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= m; j++) {
				if (((i+j)&1) and output[i][j] == 1){output[i][j] = 2;}
				else if (((i+j)&1) and output[i][j] == 2){output[i][j] = 1;}
				if (output[i][j] == 1){cout << 'W';}
				else{cout << 'B';}
			} cout << '\n';
		}
	}
}

}int main()
{
	#ifndef ONLINE_JUDGE
	freopen("in.in" , "r" , stdin);
	#endif
	ios :: sync_with_stdio(0);
	cin.tie(0) , cout.tie(0);
	return Slongod :: main(),0;
}