fix: update for jdk21

build.gradle.kts

@@ -9,6 +9,7 @@ version = "1.3.0"
 
 val invuiVersion: String = "1.46"
 val jacksonVersion: String = "2.20.0"
+val mockBukkitVersion: String = "4.72.8"
 
 java {
     sourceCompatibility = JavaVersion.VERSION_21
@@ -20,8 +21,8 @@ java {
 }
 
 repositories {
-    mavenCentral()
     mavenLocal()
+    mavenCentral()
 
     maven("https://repo.xenondevs.xyz/releases")
     maven("https://repo.papermc.io/repository/maven-public/")
@@ -47,9 +48,20 @@ dependencies {
     implementation("org.mariadb.jdbc:mariadb-java-client:3.5.2")
     implementation("redis.clients:jedis:5.2.0")
     implementation("com.google.code.gson:gson:2.13.1")
+
+    testImplementation("org.mockbukkit.mockbukkit:mockbukkit-v1.21:$mockBukkitVersion")
+    testImplementation(platform("org.junit:junit-bom:5.13.4"))
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
 }
 
 tasks {
+    test {
+        useJUnitPlatform()
+        testLogging {
+            events("passed", "skipped", "failed")
+        }
+    }
 
     processResources {
         from("src/main/resources")

src/main/java/xyz/ineanto/nicko/Nicko.java

@@ -40,6 +40,10 @@ public class Nicko extends JavaPlugin {
     private PlayerNameStore nameStore;
     private RandomNameFetcher nameFetcher;
 
+    public Nicko() {
+        super();
+    }
+
     @Override
     public void onLoad() {
         PacketEvents.setAPI(SpigotPacketEventsBuilder.build(this));

src/main/java/xyz/ineanto/nicko/gui/items/admin/ManageCacheItem.java

@@ -22,7 +22,7 @@ public class ManageCacheItem extends AsyncItem {
         super(new SuppliedItem(() -> {
                     final ItemBuilder builder = new ItemBuilder(Material.PAINTING);
                     return playerLanguage.translateItem(builder, LanguageKey.GUI.LOADING);
-                }, (_ -> true)).getItemProvider(),
+                }, (click -> true)).getItemProvider(),
                 () -> {
                     AbstractItemBuilder<?> builder;
 

src/main/java/xyz/ineanto/nicko/gui/items/admin/ManagePlayerItem.java

@@ -22,7 +22,7 @@ public class ManagePlayerItem {
         return new SuppliedItem(() -> {
             final ItemBuilder builder = new ItemBuilder(Material.WRITABLE_BOOK);
             return playerLanguage.translateItem(builder, LanguageKey.GUI.Admin.MANAGE_PLAYER);
-        }, _ -> {
+        }, click -> {
             new PlayerCheckGUI(player, Bukkit.getOnlinePlayers()).open();
             return true;
         });

src/main/java/xyz/ineanto/nicko/gui/items/admin/cache/CacheEntryItem.java

@@ -33,7 +33,7 @@ public class CacheEntryItem extends AsyncItem {
         super(new SuppliedItem(() -> {
                     final ItemBuilder builder = new ItemBuilder(Material.PAINTING);
                     return playerLanguage.translateItem(builder, LanguageKey.GUI.LOADING);
-                }, (_ -> true)).getItemProvider(),
+                }, (click -> true)).getItemProvider(),
                 () -> {
                     final String dashedUuid = uuid.replaceAll("(.{8})(.{4})(.{4})(.{4})(.+)", "$1-$2-$3-$4-$5");
                     final UUID uuidObject = UUID.fromString(dashedUuid);

src/main/java/xyz/ineanto/nicko/gui/items/admin/check/PlayerInformationItem.java

@@ -36,7 +36,7 @@ public class PlayerInformationItem extends AsyncItem {
         super(new SuppliedItem(() -> {
             final ItemBuilder builder = new ItemBuilder(Material.PAINTING);
             return playerLanguage.translateItem(builder, LanguageKey.GUI.LOADING);
-        }, (_ -> true)).getItemProvider(), () -> {
+        }, (click -> true)).getItemProvider(), () -> {
             try {
                 final SkullBuilder skull = new SkullBuilder(target.getUniqueId());
                 final Optional<NickoProfile> optionalProfile = Nicko.getInstance().getDataStore().getData(target.getUniqueId());

src/main/java/xyz/ineanto/nicko/gui/items/favorites/FavoriteAppearanceEntryItem.java

@@ -29,7 +29,7 @@ public class FavoriteAppearanceEntryItem extends AsyncItem {
         super(new SuppliedItem(() -> {
                     final ItemBuilder builder = new ItemBuilder(Material.PAINTING);
                     return playerLanguage.translateItem(builder, LanguageKey.GUI.LOADING);
-                }, (_ -> true)).getItemProvider(),
+                }, (click -> true)).getItemProvider(),
                 () -> {
                     try {
                         // TODO (Ineanto, 08/06/2025): set a default skin if the entry contains only a name

src/test/java/xyz/ineanto/nicko/test/TestPluginMock.java

@@ -0,0 +1,4 @@
+package xyz.ineanto.nicko.test;
+
+public class TestPluginMock {
+}