Fix custom player provider usage for junit (#81)

* Add possibility for custom player provider

* Improve documentation for custom player provider method at test connection

testing/src/main/java/net/minestom/testing/TestConnection.java

@@ -3,16 +3,60 @@
 import net.minestom.server.coordinate.Pos;
 import net.minestom.server.entity.Player;
 import net.minestom.server.instance.Instance;
+import net.minestom.server.network.PlayerProvider;
 import net.minestom.server.network.packet.server.ServerPacket;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.concurrent.CompletableFuture;
 
+/**
+ * Represents a connection to a test server.
+ */
 public interface TestConnection {
+
+    /**
+     * Sets the custom player provider for this test connection.
+     * <br>
+     * For a successful test you need to override the sendChunk method in the player implementation.
+     * Example:
+     * <pre>{@code
+     * public class CustomGamePlayerImpl extends Player {
+     *    public CustomGamePlayerImpl(UUID uuid, String username, PlayerConnection playerConnection) {
+     *      super(uuid, username, playerConnection);
+     *    }
+     *    @Override
+     *    public void sendChunk(Chunk chunk) {
+     *      sendPacket(chunk.getFullDataPacket());
+     *    }
+     * }
+     * }</pre>
+     * @param provider the custom player provider
+     */
+    void setCustomPlayerProvider(@NotNull PlayerProvider provider);
+
+    /**
+     * Connects a player to the server.
+     *
+     * @param instance the instance to spawn the player in
+     * @param pos      the position to spawn the player at
+     * @return a future that completes when the player is connected
+     */
     @NotNull CompletableFuture<@NotNull Player> connect(@NotNull Instance instance, @NotNull Pos pos);
 
+    /**
+     * Tracks incoming packets of a specific type.
+     *
+     * @param type the packet type to track
+     * @param <T>  the packet type
+     * @return a collector for the tracked packets
+     */
     <T extends ServerPacket> @NotNull Collector<T> trackIncoming(@NotNull Class<T> type);
 
+    /**
+     * Tracks all incoming packets.
+     *
+     * @return a collector for all incoming packets
+     */
     default @NotNull Collector<ServerPacket> trackIncoming() {
         return trackIncoming(ServerPacket.class);
     }

testing/src/main/java/net/minestom/testing/TestConnectionImpl.java

@@ -8,6 +8,7 @@
 import net.minestom.server.event.player.AsyncPlayerConfigurationEvent;
 import net.minestom.server.instance.Instance;
 import net.minestom.server.network.ConnectionState;
+import net.minestom.server.network.PlayerProvider;
 import net.minestom.server.network.packet.server.SendablePacket;
 import net.minestom.server.network.packet.server.ServerPacket;
 import net.minestom.server.network.packet.server.configuration.SelectKnownPacksPacket;
@@ -18,26 +19,31 @@
 import java.net.SocketAddress;
 import java.util.List;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CopyOnWriteArrayList;
 
 final class TestConnectionImpl implements TestConnection {
-    private final Env env;
     private final ServerProcess process;
     private final PlayerConnectionImpl playerConnection = new PlayerConnectionImpl();
+    private volatile Optional<PlayerProvider> playerProvider = Optional.of(TestPlayerImpl::new);
 
     private final List<IncomingCollector<ServerPacket>> incomingTrackers = new CopyOnWriteArrayList<>();
 
     TestConnectionImpl(Env env) {
-        this.env = env;
         this.process = env.process();
     }
 
+    @Override
+    public void setCustomPlayerProvider(@NotNull PlayerProvider provider) {
+        this.playerProvider = Optional.ofNullable(provider);
+    }
+
     @Override
     public @NotNull CompletableFuture<Player> connect(@NotNull Instance instance, @NotNull Pos pos) {
         // Use player provider to disable queued chunk sending
-        process.connection().setPlayerProvider(TestPlayerImpl::new);
+        process.connection().setPlayerProvider(playerProvider.orElse(TestPlayerImpl::new));
 
         playerConnection.setConnectionState(ConnectionState.LOGIN);
         var player = process.connection().createPlayer(playerConnection, UUID.randomUUID(), "RandName");