#include <bits/stdc++.h>

using namespace std;
typedef long long LL;
const int N = 100010, M = 2e6 + 10, INF = 1e8;

int n, m, S, T;
int h[N], e[M], f[M], ne[M], idx;
int q[N], d[N], cur[N];
char g[110][110];
int dx[] = {0, 0, 1, 1}, dy[] = {0, 1, 0, 1};
int dx2[] = {0, 0, 1, 1, 1, -1, -1, -1},
    dy2[] = {1, -1, 0, 1, -1, 0, 1, -1};
bool st[N];

void add(int a, int b, int c) {
    e[idx] = b, f[idx] = c, ne[idx] = h[a], h[a] = idx++;
    e[idx] = a, f[idx] = 0, ne[idx] = h[b], h[b] = idx++;
}

bool bfs() {
    int hh = 0, tt = 0;
    memset(d, -1, sizeof d);
    q[0] = S, d[S] = 0, cur[S] = h[S];
    while (hh <= tt) {
        int t = q[hh++];
        for (int i = h[t]; ~i; i = ne[i]) {
            int ver = e[i];
            if (d[ver] == -1 && f[i]) {
                d[ver] = d[t] + 1;
                cur[ver] = h[ver];
                if (ver == T)  return 1;
                q[ ++ tt] = ver;
            }
        }
    }
    return false;
}

int find(int u, int limit) {
    if (u == T) return limit;
    int flow = 0;
    for (int i = cur[u]; ~i && flow < limit; i = ne[i]) {
        cur[u] = i;
        int ver = e[i];
        if (d[ver] == d[u] + 1 && f[i]) {
            int t = find(ver, min(f[i], limit - flow));
            if (!t) d[ver] = -1;
            f[i] -= t, f[i ^ 1] += t, flow += t;
        }
    }
    return flow;
}

int dinic() {
    int r = 0, flow;
    while (bfs()) while (flow = find(S, INF)) r += flow;
    return r;
}

int get(int x, int y, int type) {
    return x * m + y + type * n * m;
}

bool checkb(int x, int y) {
    for (int i = 0; i < 4; ++i) if (g[x + dx[i]][y + dy[i]] == 'W') return 0;
    return 1;
}

bool checkw(int x, int y) {
    for (int i = 0; i < 4; ++i) if (g[x + dx[i]][y + dy[i]] == 'B') return 0;
    return 1;
}

void dfs(int u) {
    st[u] = 1;
    for (int i = h[u]; ~i; i = ne[i]) {
        int j = e[i];
        if (!st[j] && f[i]) dfs(j);
    }
}

void solve() {
    scanf("%d%d", &n, &m);
    S = N - 2, T = N - 1;
    idx = 0;
    h[S] = h[T] = -1;
    for (int i = 0; i < n; ++i) scanf("%s", g[i]);
    for (int i = 0; i < n; ++i)
        for (int j = 0; j < m; ++j) {
            if (i + j & 1 && g[i][j] != '?') g[i][j] = 'B' + 'W' - g[i][j];
            h[get(i, j, 0)] = h[get(i, j, 1)] = -1;
            st[get(i, j, 0)] = st[get(i, j, 1)] = 0;
        }
    int tot = 0;
    for (int i = 0; i < n - 1; ++i)
        for (int j = 0; j < m - 1; ++j) {
            if (checkb(i, j)) add(S, get(i, j, 0), 1), ++tot;
            if (checkw(i, j)) add(get(i, j, 1), T, 1), ++tot;
            add(get(i, j, 0), get(i, j, 1), INF);
            for (int k = 0; k < 8; ++k) {
                int x = i + dx2[k], y = j + dy2[k];
                if (x >= n - 1 || y >= m - 1) continue;
                add(get(i, j, 0), get(x, y, 1), INF);
            }
        }
    printf("%d\n", tot - dinic());
    dfs(S);
    for (int i = 0; i < idx; i += 2) {
        int u = e[i ^ 1], v = e[i];
        if (st[u] == st[v])
            if (u == S) {
                int x = v / m, y = v % m;
                if (!checkb(x, y)) continue;
                for (int j = 0; j < 4; ++j)
                    g[x + dx[j]][y + dy[j]] = 'B';
            }
            else if (v == T) {
                u -= n * m;
                int x = u / m, y = u % m;
                if (!checkw(x, y)) continue;
                for (int j = 0; j < 4; ++j)
                    g[x + dx[j]][y + dy[j]] = 'W';
            }
    }
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) 
            if (g[i][j] == '?') putchar('B');
            else if (i + j & 1) putchar('B' + 'W' - g[i][j]);
            else putchar(g[i][j]);
        puts("");
    }
}

int main() {
    int tcase;
    scanf("%d", &tcase);
    while (tcase--) solve();
}