feat: 테스트 핑퐁 리스너 추가

src/main/java/com/gdschongik/gdsc/domain/discord/listener/PingpongListener.java

@@ -0,0 +1,30 @@
+package com.gdschongik.gdsc.domain.discord.listener;
+
+import com.gdschongik.gdsc.global.discord.Listener;
+import lombok.extern.slf4j.Slf4j;
+import net.dv8tion.jda.api.entities.Message;
+import net.dv8tion.jda.api.entities.User;
+import net.dv8tion.jda.api.entities.channel.concrete.TextChannel;
+import net.dv8tion.jda.api.events.message.MessageReceivedEvent;
+import net.dv8tion.jda.api.hooks.ListenerAdapter;
+
+@Slf4j
+@Listener
+public class PingpongListener extends ListenerAdapter {
+
+    @Override
+    public void onMessageReceived(MessageReceivedEvent event) {
+        User author = event.getAuthor();
+        TextChannel channel = event.getChannel().asTextChannel();
+        Message message = event.getMessage();
+        String content = message.getContentRaw(); // get only textual content of message
+
+        log.info("Message from {} in {}: {}", author.getName(), channel.getName(), message.getContentDisplay());
+
+        if (author.isBot()) return;
+
+        if (content.equals("!ping")) {
+            channel.sendMessage("Pong!").queue();
+        }
+    }
+}