import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;


public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        solve(in, out);
        out.close();
    }

    static String reverse(String s) {
        return (new StringBuilder(s)).reverse().toString();
    }

    static void sort(int ar[]) {
        int n = ar.length;
        ArrayList<Integer> a = new ArrayList<>();
        for (int i = 0; i < n; i++)
            a.add(ar[i]);
        Collections.sort(a);
        for (int i = 0; i < n; i++)
            ar[i] = a.get(i);
    }

    static long ncr(long n, long r, long mod) {
        if (r == 0)
            return 1;
        long val = ncr(n - 1, r - 1, mod);
        val = (n * val) % mod;
        val = (val * modInverse(r, mod)) % mod;
        return val;
    }

    

    public static void solve(InputReader sc, PrintWriter pw) {
        int i, j = 0;
        // int t = 1;
        int t = sc.nextInt();
        u: while (t-- > 0) {
            int n=sc.nextInt();
            int m=sc.nextInt();
            char ch[][]=new char[n][m];
            for(i=0;i<n;i++){
                ch[i]=sc.next().toCharArray();
            }
            for(i=0;i<n;i++){
                for(j=0;j<m;j++){
                    if(ch[i][j]=='B'){
                        if(i>0&&ch[i-1][j]=='G'){
                            pw.println("No");
                            continue u;
                        }
                        if(j>0&&ch[i][j-1]=='G'){
                            pw.println("No");
                            continue u;
                        }
                        if(i<n-1&&ch[i+1][j]=='G'){
                            pw.println("No");
                            continue u;
                        }
                        if(j<m-1&&ch[i][j+1]=='G'){
                            pw.println("No");
                            continue u;
                        }
                        if(i>0&&ch[i-1][j]=='.'){
                            ch[i-1][j]='#';
                        }
                        if(j>0&&ch[i][j-1]=='.'){
                            ch[i][j-1]='#';
                        }
                        if(i<n-1&&ch[i+1][j]=='.'){
                            ch[i+1][j]='#';
                        }
                        if(j<m-1&&ch[i][j+1]=='.'){
                            ch[i][j+1]='#';
                        }
                    }
                }
            }
            int vis[][]=new int[n][m];
            fill(ch,n-1,m-1,vis,n,m);
            for(i=0;i<n;i++){
                for(j=0;j<m;j++){
                    if(ch[i][j]=='G'){
                        int f=0;
                        if(i>0&&(ch[i-1][j]=='R'||ch[i-1][j]=='G')){
                            f++;
                        }
                        else if(j>0&&(ch[i][j-1]=='R'||ch[i][j-1]=='G')){
                            f++;
                        }
                        else if(i<n-1&&(ch[i+1][j]=='R'||ch[i+1][j]=='G')){
                            f++;
                        }
                        else if(j<m-1&&(ch[i][j+1]=='R'||ch[i][j+1]=='G')){
                            f++;
                        }
                        if(f==0){
                            pw.println("No");
                            continue u;
                        }
                    }
                }
            }
            pw.println("Yes");
        }
    }

    static void fill(char ch[][], int i, int j, int vis[][], int n, int m){
        if(i>=n||j>=m||i<0||j<0||vis[i][j]==1)
            return;
        vis[i][j]=1;
        if(ch[i][j]=='#')
            return;
        if(ch[i][j]=='.')
            ch[i][j]='R';
        fill(ch,i-1,j,vis,n,m);
        fill(ch,i+1,j,vis,n,m);
        fill(ch,i,j-1,vis,n,m);
        fill(ch,i,j+1,vis,n,m);
    }

    static class Pair implements Comparable<Pair> {
        int a;
        int b;
        int c;
        
        Pair(int a, int b, int c) {
            this.a = a;
            this.b = b;
            this.c = c;
        }

        public int compareTo(Pair p) {
            if (c != p.c)
                return -1*(c - p.c);
            return (a - p.a);
        }
    }

    static boolean isPrime(long n) {
        if (n <= 1)
            return false;
        if (n <= 3)
            return true;
        if (n % 2 == 0 || n % 3 == 0)
            return false;
        for (int i = 5; i * i <= n; i = i + 6)
            if (n % i == 0 || n % (i + 2) == 0)
                return false;
        return true;
    }

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

    static long fast_pow(long base, long n, long M) {
        if (n == 0)
            return 1;
        if (n == 1)
            return base % M;
        long halfn = fast_pow(base, n / 2, M);
        if (n % 2 == 0)
            return (halfn * halfn) % M;
        else
            return (((halfn * halfn) % M) * base) % M;
    }

    static long modInverse(long n, long M) {
        return fast_pow(n, M - 2, M);
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

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

