#include<bits/stdc++.h>
#define int long long 
#define ll long long
#define pii pair<int, int>
#define inf 1e9
using namespace std;
const int N = 2e5 + 999;
int S, T, cnt, n, m, ok[N];
inline int Id(int x, int y){
    return (x - 1) * m + y;
}
struct Edge{
    int v, nxt, w;
}edge[20 * N];
int head[N], used[N], tot, cur[N], dist[N];
void add(int u, int v, int w, int t = 1){
    edge[++tot] = {v, head[u], w};
    head[u] = tot;
    if(t) add(v, u, 0, 0);
}
bool bfs(){
    for(int i = 1; i <= cnt; i++) used[i] = 0;
    used[T] = 1;
    queue<int> q;
    q.push(T);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        for(int i = head[u]; i; i = edge[i].nxt){
            int v = edge[i].v;
            if(used[v] || !edge[i ^ 1].w) continue;
            used[v] = 1;
            dist[v] = dist[u] + 1;
            q.push(v);
        }
    }
    if(!used[S]) return 0;
    for(int i = 1; i <= cnt; i++)
        cur[i] = head[i]; 
    return 1;
}
int dfs(int u, int rest){
    if(u == T) return rest;
    int sum = 0;
    for(int &i = cur[u]; i; i = edge[i].nxt){
        if(dist[u] == dist[edge[i].v] + 1 && edge[i].w){
            int ret = dfs(edge[i].v, min(rest, edge[i].w));
            rest -= ret;
            sum += ret;
            edge[i].w -= ret;
            edge[i ^ 1].w += ret;
            if(rest == 0) return sum;
        }
    }
    return sum;
}
int denic(){
    int ans = 0;
    while(bfs()) 
       ans += dfs(S, inf);
    return ans;
}
void dfs(int u){
    ok[u] = 1;
    for(int i = head[u]; i; i = edge[i].nxt){
        int v = edge[i].v;
        if(ok[v] || edge[i].w == 0) continue;
        dfs(v);
    }
}
void solve(){
    cin >> n >> m;
    S = n * m + 1, T = S + 1;
    cnt = T;
    tot = 1;
    for(int i = 1; i <= n; i++){
        string st;
        cin >> st;
        for(int j = 0; j < m; j++){
            int id = (i - 1) * m + j + 1;
            if((i + j) % 2 == 0){
                if(st[j] == 'B'){
                    st[j] = 'W';
                }
                else if(st[j] == 'W') st[j] = 'B';
            }
            if(st[j] == 'W') add(S, id, inf);
            else if(st[j] == 'B') add(id, T, inf);
        }
    }
    for(int i = 1; i < n; i++){
        for(int j = 1; j < m; j++){
            cnt++;
            add(S, cnt, 1);
            add(cnt, Id(i, j), inf);
            add(cnt, Id(i, j + 1), inf);
            add(cnt, Id(i + 1, j), inf);
            add(cnt, Id(i + 1, j + 1), inf);

            cnt++;
            add(cnt, T, 1);
            add(Id(i, j), cnt, inf);
            add(Id(i, j + 1), cnt, inf);
            add(Id(i + 1, j), cnt, inf);
            add(Id(i + 1, j + 1), cnt, inf); 
        }
    }
    int ans = cnt - T - denic();
    cout << ans << '\n';
    dfs(S);   
    for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++){
            int id = Id(i, j);
            if((i + j) % 2 == 1) ok[id] ^= 1;
            if(ok[id]) cout << "W";
            else cout << "B";
        }
        cout << '\n';
    }
    for(int i = 1; i <= cnt; i++)
        ok[i] = head[i] = cur[i] = dist[i] = 0; 
}

signed main(){
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t=1;
    cin>>t;
    while(t--)
    solve();

    return 0;
}