done (untested code)

build.ps1

@@ -0,0 +1,10 @@
+# Check if the test_server directory exists, if not, create it
+if (-not (Test-Path -Path test_server)) {
+    New-Item -ItemType Directory -Path test_server
+}
+
+# mvn clean package dependency:copy -DskipTests -DoutputDirectory=test_server/plugins
+
+Set-Location -Path test_server
+java -jar server.jar -nogui
+Set-Location -Path ..

src/main/java/rip/iwakura/civilcore/PlayerHandler.java

@@ -15,7 +15,7 @@ import rip.iwakura.civilcore.types.DbPlayer;
 
 public class PlayerHandler implements Listener {
 
-  private CivilCore civilCore = null;
+  private final CivilCore civilCore;
 
   public PlayerHandler(CivilCore civilCore) {
     this.civilCore = civilCore;
@@ -33,7 +33,7 @@ public class PlayerHandler implements Listener {
     String prefix = (inTeamChat ? ChatColor.DARK_BLUE + "TC " + ChatColor.RESET : "") 
       + (dbPlayer.team.prefix == null ?
         "" : 
-        ChatColor.translateAlternateColorCodes('&', dbPlayer.team.prefix) + " ");
+        ChatColor.translateAlternateColorCodes('&', "[" + dbPlayer.team.prefix + "]") + " ");
     String message = String.format("%s%s: %s", prefix, player_name, e.getMessage()); 
 
     if (!inTeamChat) {

src/main/java/rip/iwakura/civilcore/commands/TeamChatCommand.java

@@ -1,47 +1,53 @@
 package rip.iwakura.civilcore.commands;
 
-import java.sql.SQLException;
-
 import org.bukkit.Bukkit;
 import org.bukkit.command.Command;
 import org.bukkit.command.CommandExecutor;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;
-import org.bukkit.event.player.PlayerEvent;
 
 import net.md_5.bungee.api.ChatColor;
+import org.jetbrains.annotations.NotNull;
 import rip.iwakura.civilcore.Utils;
 import rip.iwakura.civilcore.CivilCore;
-import rip.iwakura.civilcore.types.DbPlayer;
-import rip.iwakura.civilcore.types.Team;
+
+import java.util.Objects;
 
 public class TeamChatCommand implements CommandExecutor {
-  private CivilCore civilCore = null;
+  private final CivilCore civilCore;
 
   public TeamChatCommand(CivilCore civilCore) {
     this.civilCore = civilCore;
   }
 
   @Override
-  public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
-    args = Utils.parser(args).toArray(new String[0]);
-
-    if (!(sender instanceof Player)) return true;
-
-    Player p = (Player) sender;
+  public boolean onCommand(@NotNull CommandSender sender, @NotNull Command command, @NotNull String label, String[] args) {
+    args = Objects.requireNonNull(Utils.parser(args)).toArray(new String[0]);
 
+    if (!(sender instanceof Player p)) return true;
+    if (args.length == 0) {
       if (civilCore.teamChatRegister.contains(p)) {
         civilCore.teamChatRegister.remove(p);
-      p.sendMessage(ChatColor.RED + "Team chat has been disabled.");
+        p.sendMessage(ChatColor.GREEN + "You are now in the " + ChatColor.GOLD + "GLOBAL" + ChatColor.GREEN + " channel");
+      } else {
+        civilCore.teamChatRegister.add(p);
+        p.sendMessage(ChatColor.GREEN + "You are now in the " + ChatColor.GOLD + "TEAM" + ChatColor.GREEN + " channel");
+      }
         return true;
     }
 
-    if (civilCore.db.getPlayerByName(p.getName()).team.name == null) {
-      p.sendMessage(ChatColor.RED + "You aren't in a team :(");
-      return true;
-    }
+    String message = String.join(" ", args);
+    if (civilCore.teamChatRegister.contains(p)) {
+      civilCore.teamChatRegister.remove(p);
+      Bukkit.broadcastMessage(ChatColor.DARK_GREEN + "TEAM > " + ChatColor.GREEN + p.getName() + ": " + message);
       civilCore.teamChatRegister.add(p);
-    p.sendMessage(ChatColor.GREEN + "Team chat has been enabled.");
+    } else {
+      civilCore.teamChatRegister.add(p);
+      Bukkit.broadcastMessage(p.getName() + ": " + message);
+      civilCore.teamChatRegister.remove(p);
+    }
+
+
 
     return true;
   }