import java.io.*;
import java.util.*;
public class Main {
    public static void main(String args[])
    {
        FastReader input=new FastReader();
        PrintWriter out=new PrintWriter(System.out);
        int T=input.nextInt();
        while(T-->0)
        {
            int n=input.nextInt();
            int m=input.nextInt();
            ArrayList<Integer> adj[]=new ArrayList[n*m];
            String str[]=new String[n];
            char ch[][]=new char[n][m];
            Vertex V[]=new Vertex[n*m];
            for(int i=0;i<n;i++)
            {
                ch[i]=input.next().toCharArray();
                for(int j=0;j<m;j++)
                {
                    adj[i*m+j]=new ArrayList<>();
                    V[i*m+j]=new Vertex(i*m+j);
                }
            }
            int c=0;
            for(int i=0;i<n;i++)
            {
                for(int j=0;j<m;j++)
                {
                    if(ch[i][j]=='B')
                    {
                        if(i-1>=0 && ch[i-1][j]=='.')
                        {
                            ch[i-1][j]='#';
                        }
                        if(i+1<n && ch[i+1][j]=='.')
                        {
                            ch[i+1][j]='#';
                        }
                        if(j-1>=0 && ch[i][j-1]=='.')
                        {
                            ch[i][j-1]='#';
                        }
                        if(j+1<m && ch[i][j+1]=='.')
                        {
                            ch[i][j+1]='#';
                        }
                    }
                }
            }
            int flag=0;
            for(int i=0;i<n;i++)
            {
                for(int j=0;j<m;j++)
                {
                    if(ch[i][j]!='#')
                    {
                        if(i-1>=0 && ch[i-1][j]!='#')
                        {
                            adj[i*m+j].add((i-1)*m+j);
                        }
                        if(i+1<n && ch[i+1][j]!='#')
                        {
                            adj[i*m+j].add((i+1)*m+j);
                        }
                        if(j-1>=0 && ch[i][j-1]!='#')
                        {
                            adj[i*m+j].add((i)*m+j-1);
                        }
                        if(j+1<m && ch[i][j+1]!='#')
                        {
                            adj[i*m+j].add((i)*m+j+1);
                        }
                    }
                }
            }
            /*
            for(int i=0;i<n*m;i++)
            {
                out.println(adj[i]);
            }

             */
            flag=0;
            for(int i=0;i<n;i++)
            {
                for(int j=0;j<m;j++)
                {
                    if(ch[i][j]=='B')
                    {
                        if(i-1>=0 && ch[i-1][j]=='G')
                        {
                            flag=1;
                            break;
                        }
                        if(i+1<n && ch[i+1][j]=='G')
                        {
                            flag=1;
                            break;
                        }
                        if(j-1>=0 && ch[i][j-1]=='G')
                        {
                            flag=1;
                            break;
                        }
                        if(j+1<m && ch[i][j+1]=='G')
                        {
                            flag=1;
                            break;
                        }
                    }
                }
            }
            bfs(adj,V,n*m-1);
            for(int i=0;i<n;i++)
            {
                for(int j=0;j<m;j++)
                {
                    if(ch[i][j]=='G')
                    {
                        if(V[i*m+j].d==0)
                        {
                            flag=1;
                            break;
                        }
                    }
                }
            }
            if(flag==1)
            {
                out.println("NO");
            }
            else
            {
                out.println("YES");
            }
        }
        out.close();
    }
    public static void bfs(ArrayList<Integer> adj[],Vertex V[],int s)
    {
        V[s].color="gray";
        V[s].d=0;
        V[s].parent=null;
        Queue<Integer> q=new LinkedList<>();
        q.add(s);
        while(!q.isEmpty())
        {
            int k=q.poll();
            Vertex u=V[k];
            for(int i=0;i<adj[k].size();i++)
            {
                int key=adj[k].get(i);
                Vertex v=V[key];
                if(v.color=="white")
                {
                    q.add(key);
                    v.color="gray";
                    v.d=u.d+1;
                    v.parent=u;
                }
            }
            u.color="black";
        }
    }
    static Boolean isReachable(ArrayList<Integer> adj[],int s, int d)
    {
        boolean visited[] = new boolean[adj.length];
        Queue<Integer> queue=new LinkedList<>();
        visited[s]=true;
        queue.add(s);
        Iterator<Integer> i;
        while (queue.size()!=0)
        {
            s = queue.poll();

            int n;
            i = adj[s].listIterator();
            while (i.hasNext())
            {
                n = i.next();
                if (n==d)
                    return true;
                if (!visited[n])
                {
                    visited[n] = true;
                    queue.add(n);
                }
            }
        }
        return false;
    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}
class Vertex
{
    int key;
    int d,f;
    String color;
    Vertex parent;
    Vertex(int key)
    {
        this.key=key;
        this.d=0;
        this.f=0;
        this.color="white";
        this.parent=null;
    }
}