Added test class

pom.xml

@@ -33,7 +33,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <java.version>17</java.version>
-        <powermock.version>1.7.4</powermock.version>
+        <powermock.version>2.0.9</powermock.version>
         <!-- More visible way how to change dependency versions -->
         <spigot.version>1.20.4-R0.1-SNAPSHOT</spigot.version>
         <bentobox.version>2.0.0-SNAPSHOT</bentobox.version>

src/main/java/world/bentobox/extramobs/listeners/MobsSpawnListener.java

@@ -60,24 +60,25 @@ public void onEntitySpawn(CreatureSpawnEvent event)
 			this.addon.getPlugin().getIWM().getAddon(world);
 
 		if (!optionalAddon.isPresent() ||
-			!this.addon.getSettings().getDisabledGameModes().isEmpty() &&
+                (!this.addon.getSettings().getDisabledGameModes().isEmpty()
+                        &&
 				this.addon.getSettings().getDisabledGameModes().contains(
-					optionalAddon.get().getDescription().getName()))
+					optionalAddon.get().getDescription().getName())))
 		{
 			// GameMode addon is not in enable list.
 			return;
 		}
 
-
         if ((event.getEntityType().equals(EntityType.ZOMBIFIED_PIGLIN)
                 || event.getEntityType().equals(EntityType.PIGLIN))
-                &&
-			this.addon.getPlugin().getIWM().isIslandNether(world))
+                && this.addon.getPlugin().getIWM().isIslandNether(world))
 		{
+
 			// replace pigmen with blaze or wither
 
 			if (this.isSuitableNetherLocation(event.getLocation()))
 			{
+
 				if (this.spawningRandom.nextDouble() < this.addon.getSettings().getWitherSkeletonChance())
 				{
 					// oOo wither skeleton got lucky.
@@ -108,6 +109,7 @@ else if (event.getEntityType() == EntityType.ENDERMAN &&
 		}
         else if (world.getEnvironment() == World.Environment.NORMAL && event.getEntity() instanceof Fish)
 		{
+
 			// Check biome
 			Biome biome = world.getBiome(
 				event.getLocation().getBlockX(),

src/test/java/world/bentobox/extramobs/listeners/MobsSpawnListenerTest.java

@@ -0,0 +1,159 @@
+package world.bentobox.extramobs.listeners;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.util.Optional;
+
+import org.bukkit.Location;
+import org.bukkit.Material;
+import org.bukkit.World;
+import org.bukkit.block.Biome;
+import org.bukkit.block.Block;
+import org.bukkit.entity.EntityType;
+import org.bukkit.entity.Fish;
+import org.bukkit.event.entity.CreatureSpawnEvent;
+import org.eclipse.jdt.annotation.NonNull;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.powermock.modules.junit4.PowerMockRunner;
+
+import world.bentobox.bentobox.BentoBox;
+import world.bentobox.bentobox.api.addons.AddonDescription;
+import world.bentobox.bentobox.api.addons.GameModeAddon;
+import world.bentobox.bentobox.managers.IslandWorldManager;
+import world.bentobox.extramobs.ExtraMobsAddon;
+import world.bentobox.extramobs.config.Settings;
+
+@RunWith(PowerMockRunner.class)
+public class MobsSpawnListenerTest {
+
+    @Mock
+    private ExtraMobsAddon addon;
+
+    @Mock
+    private CreatureSpawnEvent event;
+
+    @Mock
+    private World world;
+
+    private MobsSpawnListener listener;
+
+    private Settings settings;
+
+    @Mock
+    private BentoBox plugin;
+
+    @Mock
+    private IslandWorldManager iwm;
+
+    @Mock
+    private GameModeAddon gma;
+
+    @Mock
+    private Location location;
+
+    @Mock
+    private Block block;
+
+    @Before
+    public void setUp() {
+        settings = new Settings();
+        when(addon.getSettings()).thenReturn(settings);
+
+        when(addon.getPlugin()).thenReturn(plugin);
+
+        when(plugin.getIWM()).thenReturn(iwm);
+
+        when(iwm.getAddon(world)).thenReturn(Optional.of(gma));
+
+        when(iwm.isIslandEnd(world)).thenReturn(true);
+        when(iwm.isIslandNether(world)).thenReturn(true);
+
+        @NonNull
+        AddonDescription desc = new AddonDescription.Builder("main", "bskyblock", "1.0.0").build();
+
+        when(gma.getDescription()).thenReturn(desc);
+
+        // Location
+        when(location.getBlock()).thenReturn(block);
+        when(location.getWorld()).thenReturn(world);
+
+        when(block.getRelative(any())).thenReturn(block);
+
+        when(block.getType()).thenReturn(Material.STONE);
+
+        // Initialize mocks and the class to test
+        listener = new MobsSpawnListener(addon);
+    }
+
+    // Test case for natural spawning of Zombified Piglin in the Nether
+    @Test
+    public void testNaturalSpawnZombifiedPiglinNether() {
+        when(event.getEntityType()).thenReturn(EntityType.ZOMBIFIED_PIGLIN);
+        when(event.getSpawnReason()).thenReturn(CreatureSpawnEvent.SpawnReason.NATURAL);
+        when(event.getLocation()).thenReturn(location);
+        when(world.getEnvironment()).thenReturn(World.Environment.NETHER);
+        when(addon.getPlugin().getIWM().isIslandNether(world)).thenReturn(true);
+        settings.setWitherSkeletonChance(1.1); // Set so that it will always spawn
+        when(block.getType()).thenReturn(Material.NETHER_BRICKS);
+
+        listener.onEntitySpawn(event);
+
+        verify(event).setCancelled(true);
+        // Additional verifications can be added to check if the correct entity was spawned
+    }
+
+    // Test case for natural spawning of Enderman in the End
+    @Test
+    public void testNaturalSpawnEndermanEnd() {
+        when(event.getEntityType()).thenReturn(EntityType.ENDERMAN);
+        when(event.getSpawnReason()).thenReturn(CreatureSpawnEvent.SpawnReason.NATURAL);
+        when(event.getLocation()).thenReturn(location);
+        when(world.getEnvironment()).thenReturn(World.Environment.THE_END);
+        when(addon.getPlugin().getIWM().isIslandEnd(world)).thenReturn(true);
+        settings.setShulkerChance(1.1); // Set so that it will always spawn
+        when(block.getType()).thenReturn(Material.PURPUR_BLOCK);
+
+        listener.onEntitySpawn(event);
+
+        verify(event).setCancelled(true);
+        // Additional verifications can be added to check if the correct entity was spawned
+    }
+
+    // Test case for spawning of Fish in Deep Ocean biome
+    @Test
+    public void testFishSpawnDeepOcean() {
+        Fish fish = mock(Fish.class);
+        when(event.getEntity()).thenReturn(fish);
+        when(event.getEntityType()).thenReturn(EntityType.TROPICAL_FISH);
+        when(event.getSpawnReason()).thenReturn(CreatureSpawnEvent.SpawnReason.NATURAL);
+        when(event.getLocation()).thenReturn(location);
+        when(world.getEnvironment()).thenReturn(World.Environment.NORMAL);
+        when(world.getBiome(anyInt(), anyInt(), anyInt())).thenReturn(Biome.DEEP_OCEAN);
+        settings.setGuardianChance(1.1); // Set so that it will always spawn
+        when(block.getType()).thenReturn(Material.WATER, Material.WATER, Material.WATER, Material.PRISMARINE);
+
+        listener.onEntitySpawn(event);
+
+        verify(event).setCancelled(true);
+        // Additional verifications for guardian spawning
+    }
+
+    // Test case for non-natural spawning
+    @Test
+    public void testNonNaturalSpawn() {
+        when(event.getSpawnReason()).thenReturn(CreatureSpawnEvent.SpawnReason.SPAWNER);
+
+        listener.onEntitySpawn(event);
+
+        verify(event, never()).isCancelled();
+    }
+
+}