import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeSet;

public class code6 {

	public static void main(String[] args) throws CloneNotSupportedException {
		// TODO Auto-generated method stub
		FastReader scn = new FastReader();
		PrintWriter out = new PrintWriter(System.out);
		int t = scn.nextInt();
		//int p = t;
		while(t-->0) {
			int n = scn.nextInt();
			int m = scn.nextInt();
			char[][] mat = new char[n][m];
			for(int i=0; i<n; i++)
				mat[i] = scn.next().toCharArray();
			
			int[][] arr2 = {
					{-1,0},{1,0},{0,-1},{0,1}
			};
			boolean ans = true;
			int tg = 0 ;
			for(int i = 0 ;i < n;i++) {
				for(int j = 0 ; j < m ;j++) {
					if(mat[i][j]=='G')
						tg++;
					if(mat[i][j]!='B')
						continue;	
					for(int  k = 0 ; k < 4 ;k++) {
					    int r = i+arr2[k][0];
					    int c = j+ arr2[k][1];
					    if(r<0 || c <0 || r >=n ||c>=m)
					    	continue;
						if(mat[r][c]=='G') {
							 ans = false;
						}else if (mat[r][c]=='B') {
							 
						}else if(mat[r][c]=='.') {
							mat[r][c]='#';
						}
					}
				}
			}
			
			
			c =0;
			dfs(mat, n-1 , m-1);
			
			if(ans && c == tg)
				out.println("Yes");
			else
				out.println("No");

				
		}
		out.flush();
	}
    static int c = 0 ;
	private static void dfs(char[][] arr, int i, int j) {
			if(i<0 || j<0 || i>=arr.length || j>=arr[0].length || arr[i][j]=='#'|| arr[i][j]=='B') {
				return;
			}
			if(arr[i][j]=='G') {
				c++;
			}
			arr[i][j]='#';
			dfs(arr , i+1 ,j );
			dfs(arr , i-1 ,j );
			dfs(arr , i ,j+1 );
			dfs(arr , i,j-1 );
			
	}

	public static void bfs (ArrayList<Integer>[] graph, int[] arr, int n, int i) {
		LinkedList<Integer> q = new LinkedList<>();
		//boolean[] vis = new boolean[n];
		for(int j=0; j<n; j++)
			arr[j] = Integer.MAX_VALUE;
		arr[i] = 0;
		q.addLast(i);
		while(!q.isEmpty()) {
			int u = q.removeFirst();
			//vis[u] = true;
			for(int j=0; j<graph[u].size(); j++) {
				if(arr[graph[u].get(j)] == Integer.MAX_VALUE) {
					arr[graph[u].get(j)] = arr[u]+1;
					q.addLast(graph[u].get(j));
				}
			}
		}
	}
	
	public static int first(ArrayList<Integer> arr, int low, int high, int x) 
    { 
        if(high >= low) 
        { 
            int mid = low + (high - low)/2; 
            if( ( mid == 0 || x > arr.get(mid-1)) && arr.get(mid) == x) 
                return mid; 
             else if(x > arr.get(mid)) 
                return first(arr, (mid + 1), high, x); 
            else
                return first(arr, low, (mid -1), x); 
        } 
    return -1; 
    } 
	static int gcd(int a, int b) 
    { 
    if (a == 0) 
        return b;  
    return gcd(b % a, a);  
    } 
      
	//public static int 
    static int lcm(int a, int b) 
    { 
        return (a*b)/gcd(a, b); 
    } 
    
    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;
		}
	}
}

	