SPIGOT-5900: Add test for the order of Material enum entries

src/test/java/org/bukkit/MaterialTest.java

@@ -3,9 +3,14 @@ package org.bukkit;
 import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 import com.google.common.collect.Maps;
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Map;
+import java.util.stream.StreamSupport;
 import net.minecraft.server.IRegistry;
 import net.minecraft.server.Item;
 import net.minecraft.server.MinecraftKey;
@@ -43,4 +48,28 @@ public class MaterialTest extends AbstractTestingBase {
 
         assertThat(materials, is(Collections.EMPTY_MAP));
     }
+
+    @Test
+    public void verifyMaterialOrder() {
+        List<Material> expectedOrder = new ArrayList<>(Material.values().length);
+
+        // Start with items in the same order as IRegistry.ITEM
+        StreamSupport.stream(IRegistry.ITEM.spliterator(), false)
+                .map(CraftMagicNumbers::getMaterial)
+                .forEach(expectedOrder::add);
+
+        // Then non-item blocks in the same order as IRegistry.BLOCK
+        StreamSupport.stream(IRegistry.BLOCK.spliterator(), false)
+                .map(CraftMagicNumbers::getMaterial)
+                .filter(block -> !block.isItem())
+                .forEach(expectedOrder::add);
+
+        // Then legacy materials in order of ID
+        Arrays.stream(Material.values())
+                .filter(Material::isLegacy)
+                .sorted(Comparator.comparingInt(Material::getId))
+                .forEach(expectedOrder::add);
+
+        assertArrayEquals(Material.values(), expectedOrder.toArray());
+    }
 }