#include <bits/stdc++.h>

const int N = 30'005;
const int M = 1'000'050;

using namespace std;

int n, m, s, t;
int head[N], cur[N], d[N], nxt[M << 1], ver[M << 1], edge[M << 1], cnt = 1;

inline void add(int u, int v, int w) {
	nxt[++cnt] = head[u], ver[cnt] = v, edge[cnt] = w, head[u] = cnt;
	nxt[++cnt] = head[v], ver[cnt] = u, edge[cnt] = 0, head[v] = cnt;
}

bool bfs() {
	std::queue<int> que;
	memset(d, 0, sizeof d);
	memcpy(cur, head, sizeof head);
	d[s] = 1;
	que.emplace(s);
	while (!que.empty()) {
		int x = que.front(); que.pop();
		for (int i = head[x]; i; i = nxt[i]) {
			int y = ver[i], w = edge[i];
			if (w && !d[y]) {
				d[y] = d[x] + 1;
				if (y == t) return true;
				que.emplace(y);
			}
		}
	}
	return false;
}

int dinic(int x, int flow) {
	if (x == t) return flow;
	int rest = flow, k;
	for (int &i = cur[x]; i; i = nxt[i])
		if (d[ver[i]] == d[x] + 1 && edge[i]) {
			k = dinic(ver[i], std::min(edge[i], rest)); 
			edge[i] -= k;
			edge[i ^ 1] += k;
			rest -= k;
			if (!rest) break;
		}
	return flow - rest;
}

int64_t maxflow() {
	int64_t flow, mf = 0;
	while (bfs()) 
		while (flow = dinic(s, 0x3f3f3f3f))
			mf += flow;
	return mf;
}

const int K = 105;

int id[K][K][2], g[K][K], eid[K][K][2];
string mp[N];

void solve() {
	cin >> n >> m;
	for (int i = 0; i < n; ++i) {
		string s;
		cin >> s;
		mp[i] = s;
		for (int j = 0; j < m; ++j) {
			char ch = s[j];
			if (ch == '?') 
				g[i][j] = -1;
			else 
				g[i][j] = (i + j + (s[j] == 'W')) % 2;
		}
	}
	int cur = n * m + 1;
	for (int i = 0; i < n - 1; ++i)
		for (int j = 0; j < m - 1; ++j)
			for (int o : {0, 1})
				id[i][j][o] = cur++;
	s = cur, t = s + 1;
	
	memset(head, 0, sizeof head);
	cnt = 1;

	auto vid = [&](int x, int y) {
		return x * m + y + 1;
	};
	fprintf(stderr,"stage 1\n");
	for (int i = 0; i < n - 1; ++i)
		for (int j = 0; j < m - 1; ++j) {
			add(s, id[i][j][0], 1);
			for (int dx : {0, 1}) for (int dy : {0, 1}) {
				int x = i + dx, y = j + dy;
				add(id[i][j][0], vid(x, y), 0x3f3f3f3f);
				add(vid(x, y), id[i][j][1], 0x3f3f3f3f);
			}
			add(id[i][j][1], t, 1);
		}
	fprintf(stderr,"stage 2\n");
	for (int i = 0; i < n; ++i)
		for (int j = 0; j < m; ++j) {
			int o = vid(i, j);
			switch (g[i][j]) {
				case 0:
					add(s, o, 0x3f3f3f3f);
					add(o, t, 1);
					eid[i][j][1] = cnt;
					break;
				case 1:
					add(s, o, 1);
					add(o, t, 0x3f3f3f3f);
					eid[i][j][1] = cnt;
					break;
				default:
					add(s, o, 1);
					add(o, t, 1);
					eid[i][j][1] = cnt;
					break;
			}
		}
	int64_t mf = maxflow();
	int64_t ans = 2 * (n - 1) * (m - 1) + n * m - mf;
	
	cout << ans << '\n';
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < m; ++j) {
			int pp = (i + j + (d[vid(i, j)] == 0)) % 2;
			putchar(!pp ? 'B' : 'W');
		}
		putchar('\n');
	}
}

int main() {
	int T;
	cin >> T;
	while (T--) {
		solve();
	}	
	return 0;
}