// Skyqwq
#include <bits/stdc++.h>

using namespace std;

const int S = 105, N = S * S, M = N * 2 + N * 9, INF = 1e9;

int n, m;

char s[S][S];

typedef long long LL;

namespace MF{
    int n, m, s, t, pre[N], cur[N], q[N];
    LL res, maxflow, d[N];
    int head[N], numE = 1;
    struct E{
        int next, v, w;
    } e[M << 1];
    
    void inline add(int u, int v, int w) {
        e[++numE] = (E) { head[u], v, w };
        head[u] = numE;
    }
    void inline init(int v, int a, int b) {
        for (int i = 1; i <= n; i++) head[i] = 0;
        numE = 1;
        n = v, s = a, t = b;
    }
    
    bool inline bfs() {
        int hh = 0, tt = -1;
        for (int i = 1; i <= n; i++) d[i] = 0;
        q[++tt] = s, d[s] = 1, cur[s] = head[s];
        while (hh <= tt) {
            int u = q[hh++];
            for (int i = head[u]; i; i = e[i].next) {
                int v = e[i].v;
                if (!d[v] && e[i].w) {
                    cur[v] = head[v];
                    q[++tt]= v, d[v] = d[u] + 1;
                    if (v == t) return 1;
                }
            }
        }
        return 0;
    }
    LL dinic(int u, LL flow) {
        if (u == t) return flow;
        LL rest = flow;
        for (int i = cur[u]; i && rest; i = e[i].next) {
            cur[u] = i;
            int v = e[i].v;
            if (e[i].w&& d[v] == d[u] + 1) {
                int k = dinic(v, min((LL)e[i].w, rest));
                if (!k) d[v] = 0;
                rest -= k, e[i].w -= k,e[i ^ 1].w += k;
            }
        }
        return flow - rest;
    }
    void inline addE(int u, int v, int w) {
        add(u, v, w), add(v, u, 0);
    }
    LL inline work() {
        maxflow = 0;
        while (bfs())
            while (res = dinic(s, INF)) maxflow += res;
        return maxflow; 
    }
    // Find min-cut 
    bool vis[N];
    
    void dfs(int u) {
        //cerr << u << " dfs\n";
        vis[u] = 1;
        for (int i = head[u]; i; i = e[i].next) {
            int v = e[i].v;
            if (!vis[v] && e[i].w) dfs(v);
        }
    }
    
    void minCut() {
        for (int i = 1; i <= n; i++) vis[i] = 0;
        dfs(s);
    }
}

int id[S][S][2], idx;

char c[2] = {'W' , 'B'};

bool chk(char cr, char y) {
    return y == '?' || cr == y;
}

bool inline chk(int x, int y, int w) {
    char cr = c[w];
    return chk(cr, s[x][y]) && chk(cr, s[x][y - 1]) && chk(cr, s[x - 1][y]) && chk(cr, s[x - 1][y - 1]);
}

void clr() {
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) id[i][j][0] = id[i][j][1] = 0;
    idx = 0;
}

void fl(int x, int y, int z) {

    for (int i = x - 1; i <= x; i++)
        for (int j = y - 1; j <= y; j++) {
            if (s[i][j] != '?' && s[i][j] != c[z]) assert(false);
            s[i][j] = c[z];
        }
}

int main() {
    int T; scanf("%d", &T);
    while (T--) {
        scanf("%d%d", &n, &m);
        for (int i = 1; i <= n; i++) {
            scanf("%s", s[i] + 1);
            for (int j = 1; j <= m; j++) {
                if ((i + j) & 1) {
                    if (s[i][j] == 'W') s[i][j] = 'B';
                    else if (s[i][j] == 'B') s[i][j] = 'W';
                }
            }
        }

        // for (int i = 1; i <= n; i++) {
        //     for (int j = 1; j <= m; j++) {
        //         cout << s[i][j];
        //     }
        //     cout << endl;
        // }

        for (int i = 2; i <= n; i++) {
            for (int j = 2; j <= m; j++) {
                for (int z = 0; z < 2; z++) {
                    if (chk(i, j, z))
                        id[i][j][z] = ++idx;                        
                }
            }
        }
        int ans = idx;
        // cout << ans << endl;
        int st = ++idx, t = ++idx;
        MF::init(idx, st, t);
        for (int i = 2; i <= n; i++) {
            for (int j = 2; j <= m; j++) {
                if (id[i][j][0]) {
                    MF::addE(st, id[i][j][0], 1);
                    for (int x = max(i - 1, 2); x <= min(i + 1, n); x++) {
                        for (int y = max(j - 1, 2); y <= min(j + 1, m); y++) {
                            if (id[x][y][1])
                                MF::addE(id[i][j][0], id[x][y][1], INF);
                        }
                    }
                } 
                if (id[i][j][1]) {
                    MF::addE(id[i][j][1], t, 1);
                }
            }
        }
        ans -= MF::work();
        MF::minCut();
        printf("%d\n", ans);
        

        for (int i = 2; i <= n; i++) {
            for (int j = 2; j <= m; j++) {
                if (id[i][j][0] && MF::vis[id[i][j][0]])
                    fl(i, j, 0);
                if (id[i][j][1] && !MF::vis[id[i][j][1]])
                    fl(i, j, 1);   
            }
        }

        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if (s[i][j] == '?') s[i][j] = 'W';

                int t = s[i][j];
                if ((i + j) & 1) t = t == 'W' ? 'B' : 'W';
                putchar(t); 
            }
            puts("");
        }
        clr();
    }
    return 0;
}