import java.io.*;
import java.util.*;

import java.math.*;
import java.lang.*;
 
 // Author : Yash Shah

public class D implements Runnable {


    public void run() {
       	
        InputReader sc = new InputReader(System.in);
        PrintWriter out = new PrintWriter(System.out);
 
        int t=sc.nextInt();

        int xx[]={0,0,1,-1};
        int yy[]={-1,1,0,0};
        

        while(t--!=0)
        {
            int n=sc.nextInt();
            int m=sc.nextInt();
            
            char a[][] = new char[n][m];

            for(int i=0;i<n;i++)
            {
                a[i]=sc.next().toCharArray();
            }

            if(a[n-1][m-1]=='B')
            {
                out.println("No");
                continue;
            }
            boolean done=true;
            for(int i=0;done&&i<n;i++)
            {
                for(int j=0;done&&j<m;j++)
                {
                    if(a[i][j]=='B')
                    {
                        for(int k=0;done&&k<4;k++)
                        {
                            int aa=i+xx[k];
                            int bb=j+yy[k];
                            if(aa>=0 && bb>=0 && aa<n && bb<m)
                            {
                                if(a[aa][bb]=='G')
                                {
                                    out.println("No");
                                    done=false;
                                }        
                                else
                                    a[aa][bb]='#';                       
                            }
                            
                        }     
                    }
                }
            }
            if(!done)continue;
            boolean fff=true;
            for(int i=0;i<n&&fff;i++)
            {
                for(int j=0;j<m&&fff;j++)
                {
                    if(a[i][j]=='G')
                    {
                        Stack<Pair> s=new Stack<>();
                        s.push(new Pair(i,j));
                        boolean vis[][]=new boolean[n][m];
                        vis[i][j]=true;
                        while(s.size()>0)
                        {
                            Pair tmp = s.pop();
                            for(int k=0;k<4;k++)
                            {
                                int aa=tmp.a+xx[k];
                                int bb=tmp.b+yy[k];
                                if(aa>=0 && bb>=0 && aa<n && bb<m && !vis[aa][bb] && a[aa][bb]!='#')
                                {
                                        vis[aa][bb]=true;
                                        s.push(new Pair(aa,bb));        
                                }
                                
                            }    
                        }
                        if(!vis[n-1][m-1])
                        {
                            out.println("No");
                            fff=false;
                        }
                    }
                }
            }

            if(fff)out.println("Yes");

        }


        out.close();
    }
 

//========================================================================

	static class Pair
	{
		int a,b;
		Pair(int aa,int bb)
		{
			a=aa;
			b=bb;
		}
	}
	
	static void sa(int a[],InputReader sc)
	{
		for(int i=0;i<a.length;i++)
		{
			a[i]=sc.nextInt();
		}
        Arrays.sort(a);
	}

	static class PairSort implements Comparator<Pair>
	{
		public int compare(Pair a,Pair b)
		{
			return b.b-a.b;
		}
	}


    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;
        private BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
       
        public int read() {
            if (numChars==-1)
                throw new InputMismatchException();
           
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                }
                catch (IOException e) {
                    throw new InputMismatchException();
                }
               
                if(numChars <= 0)              
                    return -1;
            }
            return buf[curChar++];
        }
     
        public String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
        public int nextInt() {
            int c = read();
           
            while(isSpaceChar(c))
                c = read();
           
            int sgn = 1;
           
            if (c == '-') {
                sgn = -1;
                c = read();
            }
           
            int res = 0;
            do {
                if(c<'0'||c>'9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
           
            return res * sgn;
        }
       
        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
           
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
                return res * sgn;
        }
       
        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
       
        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            }
            while (!isSpaceChar(c));
           
            return res.toString();
        }
     
        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
     
        public String next() {
            return readString();
        }
       
        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    public static void main(String args[]) throws Exception {
        new Thread(null, new D(),"Main",1<<27).start();
    }
}
