#include <bits/stdc++.h>
using namespace std;
struct MaxFlow {
    vector<vector<int>> G; int s, t;
    vector<int> dis, q, nw; int qh, qt;
    MaxFlow(int n, int S, int T) : \
        G(n), s(S), t(T), dis(n), q(n), nw(q) {};
    struct Edge { int u, v, w; }; vector<Edge> edg;
    void addE(int u, int v, int w1 = 1, int w2 = 0) {
        G[u].push_back(edg.size()), edg.push_back({u, v, w1});
        G[v].push_back(edg.size()), edg.push_back({v, u, w2});
    }
    void bfs() {
        fill(dis.begin(), dis.end(), 0), nw[s] = 0;
        dis[s] = 1, q[qh = qt = 0] = s;
        for(; qh <= qt; ++qh) for(int i: G[q[qh]]) {
            const auto [u, v, w] = edg[i];
            if(w && !dis[v]) dis[v] = dis[u] + 1, nw[q[++qt] = v] = 0;
        }
    }
    int dfs(int x, int mf = 0x3f3f3f3f) {
        if(x == t) return mf; int lf = mf;
        for(int &i = nw[x]; i < (int)G[x].size(); ++i) {
            int e = G[x][i]; auto &[u, v, w] = edg[e];
            if(dis[u] + 1 == dis[v] && w) {
                const int tf = dfs(v, min(w, lf)); if(!tf) continue;
                w -= tf, edg[e ^ 1].w += tf; if(!(lf -= tf)) return mf;
            }
        }
        return mf - lf;
    }
    int dinic() { int r = 0; while(bfs(), dis[t]) r += dfs(s); return r; }
};
void Solve() {
    int n, m; cin >> n >> m; vector<string> in(n);
    for(int i = 0; i < n; ++i) cin >> in[i];
    vector<vector<int>> c(n, vector<int>(m));
    for(int i = 0; i < n; ++i)
        for(int j = 0; j < m; ++j)
            c[i][j] = in[i][j] == '?' ? 3 : \
                1 + (((in[i][j] == 'B') ^ i ^ j) & 1);
    const int p = n - 1, q = m - 1;
    for(int i = 0; i < p; ++i)
        for(int j = 0; j < q; ++j)
            c[i][j] &= c[i + 1][j] & c[i][j + 1] & c[i + 1][j + 1];
    const int r = p * q, s = r << 1, t = s + 1;
    MaxFlow flow(t + 1, s, t); int tot = 0;
    const auto &id = [&](int i, int j, int c) { return c * r + i * q + j; };
    for(int i = 0; i < p; ++i)
        for(int j = 0; j < q; ++j)
            if(c[i][j] & 2) flow.addE(id(i, j, 1), t);
    const int dx[] = {-1, 0, 1, -1, 0, 1, -1, 0, 1};
    const int dy[] = {-1, -1, -1, 0, 0, 0, 1, 1, 1};
    const auto &valid = [&](int i, int j)
        { return 0 <= i && i < p && 0 <= j && j < q; };
    for(int i = 0; i < p; ++i)
        for(int j = 0; j < q; ++j)
            tot += (c[i][j] & 1) + (c[i][j] >> 1);
    for(int i = 0; i < p; ++i)
        for(int j = 0; j < q; ++j) if(c[i][j] & 1) {
            flow.addE(s, id(i, j, 0));
            for(int d = 0, to; d < 9; ++d) {
                const int I = i + dx[d], J = j + dy[d];
                if(valid(I, J) && (c[I][J] & 2))
                    flow.addE(id(i, j, 0), id(I, J, 1), 0x3f3f3f3f);
            }
        }
    printf("%d\n", tot - flow.dinic());
    for(const auto [u, v, w] : flow.edg)
        if(u == s && flow.dis[v]) {
            const int id = v, x = id / q, y = id - q * x;
            const char c0 = (x ^ y) & 1 ? 'B' : 'W';
            const char c1 = (x ^ y) & 1 ? 'W' : 'B';
            in[x][y] = in[x + 1][y + 1] = c0, in[x + 1][y] = in[x][y + 1] = c1;
        } else if(v == t && !flow.dis[u]) {
            const int id = u - r, x = id / q, y = id - q * x;
            const char c0 = (x ^ y) & 1 ? 'W' : 'B';
            const char c1 = (x ^ y) & 1 ? 'B' : 'W';
            in[x][y] = in[x + 1][y + 1] = c0, in[x + 1][y] = in[x][y + 1] = c1;
        }
    for(int i = 0; i < n; ++i)
        for(int j = 0; j < m; ++j)
            in[i][j] = in[i][j] == '?' ? 'W' : in[i][j];
    for(int i = 0; i < n; ++i) puts(in[i].c_str());
}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    int T; cin >> T; while(T--) Solve();
}