/*input
6
1 1
.
1 2
G.
2 2
#B
G.
2 3
G.#
B#.
3 3
#B.
#..
GG.
2 2
#B
B.
*/




import java.math.*;
import java.io.*;
import java.util.*;
public class Main
{
    static class Reader 
    { 
        final private int BUFFER_SIZE = 1 << 16; 
        private DataInputStream din; 
        private byte[] buffer; 
        private int bufferPointer, bytesRead;
public Reader() 
        { 
            din = new DataInputStream(System.in); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        }
public Reader(String file_name) throws IOException 
        { 
            din = new DataInputStream(new FileInputStream(file_name)); 
            buffer = new byte[BUFFER_SIZE]; 
            bufferPointer = bytesRead = 0; 
        }
public String readLine() throws IOException 
        { 
            byte[] buf = new byte[64]; // line length 
            int cnt = 0, c; 
            while ((c = read()) != -1) 
            { 
                if (c == '\n') 
                    break; 
                buf[cnt++] = (byte) c; 
            } 
            return new String(buf, 0, cnt); 
        }
public int nextInt() throws IOException 
        { 
            int ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do
            { 
                ret = ret * 10 + c - '0'; 
            }  while ((c = read()) >= '0' && c <= '9');
if (neg) 
                return -ret; 
            return ret; 
        }
public long nextLong() throws IOException 
        { 
            long ret = 0; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read(); 
            do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9'); 
            if (neg) 
                return -ret; 
            return ret; 
        }
public double nextDouble() throws IOException 
        { 
            double ret = 0, div = 1; 
            byte c = read(); 
            while (c <= ' ') 
                c = read(); 
            boolean neg = (c == '-'); 
            if (neg) 
                c = read();
do { 
                ret = ret * 10 + c - '0'; 
            } 
            while ((c = read()) >= '0' && c <= '9');
if (c == '.') 
            { 
                while ((c = read()) >= '0' && c <= '9') 
                { 
                    ret += (c - '0') / (div *= 10); 
                } 
            }
if (neg) 
                return -ret; 
            return ret; 
        }
private void fillBuffer() throws IOException 
        { 
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE); 
            if (bytesRead == -1) 
                buffer[0] = -1; 
        }
private byte read() throws IOException 
        { 
            if (bufferPointer == bytesRead) 
                fillBuffer(); 
            return buffer[bufferPointer++]; 
        }
public void close() throws IOException 
        { 
            if (din == null) 
                return; 
            din.close(); 
        } 
    } 





    static Reader sc=new Reader();
    static BufferedWriter bw=new BufferedWriter(new OutputStreamWriter(System.out));

    public static void main(String args[])throws IOException
    {
        /*
         * For integer input: int n=inputInt();
         * For long input: long n=inputLong();
         * For double input: double n=inputDouble();
         * For String input: String s=inputString();
         * Logic goes here
         * For printing without space: print(a+""); where a is a variable of any datatype
         * For printing with space: printSp(a+""); where a is a variable of any datatype
         * For printing with new line: println(a+""); where a is a variable of any datatype
		
		//all four
         int[] dr = { 1, 0, -1, 0 };
		 int[] dc = { 0, 1, 0, -1 };
         */


        	
 int[] dr = { 1, 0, -1, 0 };
 int[] dc = { 0, 1, 0, -1 };
		   
        int t=inputInt();
        while(t-- >0)
        {
        	int n=inputInt(),m=inputInt();

        	char[][] a= new char[n][m];
        	inputString();
        	for(int i=0;i<n;i++)
        	{
        		String s=inputString();

        		a[i]=s.toCharArray();
        	}

        	for(int i=0;i<n;i++)
        	{
        		for(int j=0;j<m;j++)
        		{
        			if(a[i][j]=='B')
        			{
        				for(int k=0;k<4;k++)
        				{

        					int r=i+dr[k];int c=j+dc[k];
        						if(r>=0 && r<n && c>=0 && c<m && a[r][c]=='.')
        							a[r][c]='#';
        				}
        			}
        		}
        	}

        	/*for(int i=0;i<n;i++)
        	{
        		for(int j=0;j<m;j++)
        			printSp(a[i][j]+"");
        		println("");
        	}*/

        	Queue<int[]> q = new LinkedList<>();
        	boolean visit[][] = new boolean[n][m];
        	if(a[n-1][m-1]!='#')
        	{
        		q.add(new int[]{n-1,m-1});
        		visit[n-1][m-1]=true;

        	}

        	while(!q.isEmpty())
        	{
        		int temp[]=q.poll();
        		int x=temp[0];
        		int y=temp[1];

        			visit[x][y]=true;

        			for(int i=0;i<4;i++)
        			{
        				int r=x+dr[i],c=y+dc[i];

        				if(r>=0 && r<n && c>=0 && c<m && a[r][c]!='#' && !visit[r][c])
        				{
        					visit[r][c]=true;
        					q.add(new int[]{r,c});
        				}
        			}
        	}

        	int flag=0;
        	for(int i=0;i<n;i++)
        	{

        		for(int j=0;j<m;j++)
        		{
        			if((a[i][j]=='G' && !visit[i][j]) ||  (a[i][j]=='B' && visit[i][j]))
        			{
        				flag=1;
        				break;
        			}
        		}
        	}

if(flag==1)
{
	println("No");
}
else
println("Yes");

		}

		


       bw.flush();
        bw.close();

	}



        public static long lcm(long a,long b)
        {	
        	return a / gcd(a, b) * b;
        }
        public static long gcd(long a,long b)
        {
        	if(b==0)
        		return a;
        	return gcd(b,a%b);
        }

     public static int inputInt()throws IOException
    {
        return sc.nextInt();
    }
    public static long inputLong()throws IOException
    {
        return sc.nextLong();
    }
    public static double inputDouble()throws IOException
    {
        return sc.nextDouble();
    }
    public static String inputString()throws IOException
    {
        return sc.readLine();
    }
    public static void print(String a)throws IOException
    {
        bw.write(a);
    }
    public static void printSp(String a)throws IOException
    {
        bw.write(a+" ");
    }
    public static void println(String a)throws IOException
    {
        bw.write(a+"\n");
    }
}