import java.util.InputMismatchException;
import java.util.Queue;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;

public class Main {
    InputStream is;
    PrintWriter out;
    String INPUT = "";
    
    int MAX = (int) 1e5, MOD = (int)1e9+7;
    int n,m;
    
    void solve(int TC) {
        int[] dr = { 1, 0, -1, 0 };
		    int[] dc = { 0, 1, 0, -1 };
        n = ni();m = ni();int x=0,y=0,good=0,tx=0,ty=0;
        char ch[][] = new char[n][m];
        boolean ans = true;
        for(int i=0;i<n;i++) ch[i] = ns(m);
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(ch[i][j]=='B'){
                    for(int k=0;k<4;k++){
                        x = i+dr[k];y = j+dc[k];
                        if(isValid(x,y)){
                            if(ch[x][y] == '.') ch[x][y] = '#';
                            else if(ch[x][y]=='G') ans = false;
                        }
                    }
                } else if(ch[i][j] == 'G') good++;
            }
        }
        if(good == 0) {pn("Yes");return;}
        if(ch[n-1][m-1] == '#' || !ans) {pn("No");return;};
        // BFS
        Queue<Integer> qx = new ArrayDeque<>();
        Queue<Integer> qy = new ArrayDeque<>();
        boolean vis[][] = new boolean[n][m];
        qx.add(n-1);qy.add(m-1);
        vis[n-1][m-1]=true;
        while(!qx.isEmpty()) {
            x = qx.poll();
            y = qy.poll();
            for(int i=0;i<4;i++) {
                tx = x+dr[i];
                ty = y+dc[i];
                if(isValid(tx, ty) && !vis[tx][ty]) {
                    if(ch[tx][ty] == 'G' || ch[tx][ty] == '.') {
                        qx.add(tx);
                        qy.add(ty);
                        vis[tx][ty] = true;
                    } else if(ch[tx][ty] == 'B') {pn("No");return;}
                }
            }
        }
        for(int i=0;i<n;i++) {
            for(int j=0;j<m;j++) {
                if(ch[i][j] == 'G' && !vis[i][j]) {pn("No");return;}
            }
        }
        pn("Yes");
    }
    
    boolean isValid(int p, int q){
        return p>=0 && q>=0 && p<n && q<m;
    }
    
    boolean TestCases = true;
    public static void main(String[] args) throws Exception { new Main().run(); }
    
    long pow(long a, long b) { // return pow(a,b) % MOD
        if(b==0 || a==1) return 1;
        long o = 1;
        for(long p = b; p > 0; p>>=1) {
            if((p&1)==1) o = (o*a) % MOD;
            a = (a*a) % MOD;
        } return o;
    }
    
    long inv(long x) { // return Modular Inverse of x
        long o = 1;
        for(long p = MOD-2; p > 0; p>>=1) {
            if((p&1)==1)o = (o*x)%MOD;
            x = (x*x)%MOD;
        } return o;
    }
    long gcd(long a, long b) { return (b==0) ? a : gcd(b,a%b); }
    int gcd(int a, int b) { return (b==0) ? a : gcd(b,a%b); }
    
    void run() throws Exception {
        is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        int T = TestCases ? ni() : 1;
        for(int t=1;t<=T;t++) solve(t);
        out.flush();
        if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
    }
    
    void p(Object o) { out.print(o); }
    void pn(Object o) { out.println(o); }
    void pni(Object o) { out.println(o);out.flush(); }
    double PI = 3.141592653589793238462643383279502884197169399;
    
    int ni() {
        int num = 0, b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-') {
            minus = true;
            b = readByte();
        }
        while(true) {
            if(b >= '0' && b <= '9'){
                num = num * 10 + (b - '0');
            } else {
                return minus ? -num : num;
            }
            b = readByte();
        }
    }
    
    long nl() {
        long num = 0;
        int b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-') {
            minus = true;
            b = readByte();
        }
        while(true) {
            if(b >= '0' && b <= '9') {
                num = num * 10 + (b - '0');
            } else {
                return minus ? -num : num;
            }
            b = readByte();
        }
    }
    
    double nd() { return Double.parseDouble(ns()); }
    char nc() { return (char)skip(); }
    
    int BUF_SIZE = 1024 * 8; // 1 MB is 1024*1024
    byte[] inbuf = new byte[BUF_SIZE];
    int lenbuf = 0, ptrbuf = 0;
    
    int readByte() {
        if(lenbuf == -1)throw new InputMismatchException();
        if(ptrbuf >= lenbuf){
            ptrbuf = 0;
            try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
            if(lenbuf <= 0)return -1;
        } return inbuf[ptrbuf++];
    }
    
    boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
    int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }
    
    String ns() {
        int b = skip();
        StringBuilder sb = new StringBuilder();
        while(!(isSpaceChar(b))) { // when nextLine, (b != '\n')
            sb.appendCodePoint(b); b = readByte();
        } return sb.toString();
    }
    
    char[] ns(int n) {
        char[] buf = new char[n];
        int b = skip(), p = 0;
        while(p < n && !(isSpaceChar(b))){
            buf[p++] = (char)b;
            b = readByte();
        } return n == p ? buf : Arrays.copyOf(buf, p);
    }
    
    void tr(Object... o) { if(INPUT.length() > 0)System.out.println(Arrays.deepToString(o)); }
}