Add test to ensure entities are GCed

src/test/java/net/minestom/server/api/TestUtils.java

@@ -0,0 +1,15 @@
+package net.minestom.server.api;
+
+import java.lang.ref.WeakReference;
+
+public class TestUtils {
+    public static void waitUntilCleared(WeakReference<?> ref) {
+        while (ref.get() != null) {
+            System.gc();
+            try {
+                Thread.sleep(50);
+            } catch (InterruptedException ignore) {
+            }
+        }
+    }
+}

src/test/java/net/minestom/server/entity/EntityRemovalIntegrationTest.java

@@ -7,9 +7,11 @@ import net.minestom.server.network.packet.server.play.DestroyEntitiesPacket;
 import net.minestom.server.utils.time.TimeUnit;
 import org.junit.jupiter.api.Test;
 
+import java.lang.ref.WeakReference;
 import java.time.temporal.TemporalUnit;
 import java.util.List;
 
+import static net.minestom.server.api.TestUtils.waitUntilCleared;
 import static org.junit.jupiter.api.Assertions.*;
 
 @EnvTest
@@ -61,6 +63,21 @@ public class EntityRemovalIntegrationTest {
         assertEquals(1, entity.getAliveTicks());
     }
 
+    @Test
+    public void entityGC(Env env) {
+        // Ensure that entities do not stay in memory after they are removed
+        var instance = env.createFlatInstance();
+        var entity = new Entity(EntityType.ZOMBIE);
+        entity.setInstance(instance, new Pos(0, 40, 0)).join();
+        entity.remove();
+
+        var ref = new WeakReference<>(entity);
+        //noinspection UnusedAssignment
+        entity = null;
+        env.tick(); // Required to remove the entity from the thread dispatcher
+        waitUntilCleared(ref);
+    }
+
     static final class TestEntity extends Entity {
         public TestEntity(long delay, TemporalUnit unit) {
             super(EntityType.ZOMBIE);

src/test/java/net/minestom/server/event/EventNodeMapTest.java

@@ -10,6 +10,7 @@ import org.junit.jupiter.api.Test;
 import java.lang.ref.WeakReference;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import static net.minestom.server.api.TestUtils.waitUntilCleared;
 import static org.junit.jupiter.api.Assertions.*;
 
 public class EventNodeMapTest {
@@ -81,14 +82,4 @@ public class EventNodeMapTest {
         item = null;
         waitUntilCleared(ref);
     }
-
-    private static void waitUntilCleared(WeakReference<?> ref) {
-        while (ref.get() != null) {
-            System.gc();
-            try {
-                Thread.sleep(50);
-            } catch (InterruptedException ignore) {
-            }
-        }
-    }
 }

src/test/java/net/minestom/server/instance/InstanceUnregisterIntegrationTest.java

@@ -8,6 +8,8 @@ import org.junit.jupiter.api.Test;
 
 import java.lang.ref.WeakReference;
 
+import static net.minestom.server.api.TestUtils.waitUntilCleared;
+
 @EnvTest
 public class InstanceUnregisterIntegrationTest {
 
@@ -58,14 +60,4 @@ public class InstanceUnregisterIntegrationTest {
         chunk = null;
         waitUntilCleared(ref);
     }
-
-    private static void waitUntilCleared(WeakReference<?> ref) {
-        while (ref.get() != null) {
-            System.gc();
-            try {
-                Thread.sleep(50);
-            } catch (InterruptedException ignore) {
-            }
-        }
-    }
 }