Add integration the for the custom player implementation

Author: theEvilReaper

src/test/java/net/minestom/testing/TestPlayerIntegrationTest.java

@@ -0,0 +1,29 @@
+package net.minestom.testing;
+
+import net.minestom.server.coordinate.Pos;
+import net.minestom.server.entity.Player;
+import net.minestom.server.instance.Instance;
+import net.minestom.testing.extension.MicrotusExtension;
+import org.jetbrains.annotations.NotNull;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@ExtendWith(MicrotusExtension.class)
+class TestPlayerIntegrationTest {
+
+    @Test
+    void testCustomPlayerCreation(@NotNull Env env) {
+        Instance instance = env.createFlatInstance();
+        assertNotNull(instance);
+        Player player = env.createPlayer(instance);
+        assertNotNull(player, "Player should not be null after creation");
+        assertInstanceOf(Player.class, player, "Player should be an instance of Player class");
+        assertInstanceOf(TestPlayerImpl.class, player, "Player should be an instance of TestPlayerImpl class");
+        assertEquals(instance, player.getInstance(), "Player should be in the created instance");
+        assertEquals(Pos.ZERO, player.getPosition(), "Player should start at position (0, 0, 0)");
+        assertEquals("RandName", player.getUsername(), "Player should have a random name");
+    }
+
+}