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

public class Main{
   	static void main() throws Exception{
   		int n=sc.nextInt(),m=sc.nextInt();
   		char[][]in=new char[n][m];
   		int[]dx= {0,1,0,-1},dy= {1,0,-1,0};
   		for(int i=0;i<n;i++)in[i]=sc.nextLine().toCharArray();
   		
   		
   		
   		boolean allBad=true;
   		for(int i=0;i<n;i++) {
   			for(int j=0;j<m;j++) {
   				if(in[i][j]!='G')continue;
   				//good
   				allBad=false;
   				for(int k=0;k<4;k++) {
   					int ii=i+dx[k],jj=j+dy[k];
   					if(ii<0 || ii>=n || jj<0 || jj>=m)continue;
   					if(in[ii][jj]=='B') {
   						pw.println("No");
   						return;
   					}
   				}
   			}
   		}
   		if(allBad) {
   			pw.println("Yes");
   			return;
   		}
   		
   		for(int i=0;i<n;i++) {
   			for(int j=0;j<m;j++) {
   				if(in[i][j]!='B')continue;
   				//bad
   				for(int k=0;k<4;k++) {
   					int ii=i+dx[k],jj=j+dy[k];
   					if(ii<0 || ii>=n || jj<0 || jj>=m)continue;
   					if(in[ii][jj]=='.') {
   						in[ii][jj]='#';
   					}
   				}
   			}
   		}
   		if(in[n-1][m-1]=='#') {
   			pw.println("No");
   			return;
   		}
   		boolean[][]v=new boolean[n][m];
   		LinkedList<int[]>q=new LinkedList<>();
   		q.add(new int[] {n-1,m-1});
   		v[n-1][m-1]=true;
   		while(!q.isEmpty()) {
   			int[]cur=q.poll();
   			int i=cur[0],j=cur[1];
   			for(int k=0;k<4;k++) {
				int ii=i+dx[k],jj=j+dy[k];
				if(ii<0 || ii>=n || jj<0 || jj>=m || v[ii][jj] || in[ii][jj]=='#')continue;
				v[ii][jj]=true;
				q.add(new int[] {ii,jj});
			}
   		}
   		
   		for(int i=0;i<n;i++) {
   			for(int j=0;j<m;j++) {
   				if(in[i][j]=='G' && !v[i][j]) {
   					pw.println("No");
   					return;
   				}
   			}
   		}
   		pw.println("Yes");
	}
	public static void main(String[] args) throws Exception{
		pw=new PrintWriter(System.out);
		sc = new MScanner(System.in);
		int tc=sc.nextInt();
		while(tc-->0)
			main();
		pw.flush();
	}
	static PrintWriter pw;
	static MScanner  sc;
	static class MScanner {
		StringTokenizer st;
		BufferedReader br;
		public MScanner(InputStream system) {
			br = new BufferedReader(new InputStreamReader(system));
		}
 
		public MScanner(String file) throws Exception {
			br = new BufferedReader(new FileReader(file));
		}
 
		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}
		public int[] intArr(int n) throws IOException {
	        int[]in=new int[n];for(int i=0;i<n;i++)in[i]=nextInt();
	        return in;
		}
		public long[] longArr(int n) throws IOException {
	        long[]in=new long[n];for(int i=0;i<n;i++)in[i]=nextLong();
	        return in;
		}
		public int[] intSortedArr(int n) throws IOException {
	        int[]in=new int[n];for(int i=0;i<n;i++)in[i]=nextInt();
	        shuffle(in);
	        Arrays.sort(in);
	        return in;
		}
		public long[] longSortedArr(int n) throws IOException {
	        long[]in=new long[n];for(int i=0;i<n;i++)in[i]=nextLong();
	        shuffle(in);
	        Arrays.sort(in);
	        return in;
		}
		public Integer[] IntegerArr(int n) throws IOException {
	        Integer[]in=new Integer[n];for(int i=0;i<n;i++)in[i]=nextInt();
	        return in;
		}
		public Long[] LongArr(int n) throws IOException {
	        Long[]in=new Long[n];for(int i=0;i<n;i++)in[i]=nextLong();
	        return in;
		}
		public String nextLine() throws IOException {
			return br.readLine();
		}
 
		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}
 
		public double nextDouble() throws IOException {
			return Double.parseDouble(next());
		}
 
		public char nextChar() throws IOException {
			return next().charAt(0);
		}
 
		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}
 
		public boolean ready() throws IOException {
			return br.ready();
		}
 
		public void waitForInput() throws InterruptedException {
			Thread.sleep(3000);
		}
	}
	static void shuffle(int[]in) {
		for(int i=0;i<in.length;i++) {
			int idx=(int)(Math.random()*in.length);
			int tmp=in[i];
			in[i]=in[idx];
			in[idx]=tmp;
		}
	}
	static void shuffle(long[]in) {
		for(int i=0;i<in.length;i++) {
			int idx=(int)(Math.random()*in.length);
			long tmp=in[i];
			in[i]=in[idx];
			in[idx]=tmp;
		}
	}
}