Minecraft Testing

Minecraft Testing Skill

Testing Strategies Overview

Use Java 25 for current 26.x projects. Keep legacy 1.21.x examples on Java 21 and Forge 1.20.1 on Java 17. Do not combine source layouts or APIs across lanes.

Routing Boundaries

• Use when: the task is designing or implementing automated tests (unit, mock, gametest, CI test jobs) for Minecraft projects.
• Do not use when: the task is implementing gameplay features rather than testing them (minecraft-modding, minecraft-plugin-dev, minecraft-datapack).
• Do not use when: the task is release automation or publishing pipelines (minecraft-ci-release).

Bundled References And Helpers

• Layout guide: references/test-layouts.md
• Fixture/layout validator: ./scripts/validate-test-layout.sh --root <project>

Use the validator before copying a test layout into a real project. It checks visible static dependencies, metadata, and literal structure references. It does not compile the project or prove a Game Test can run.

Unit Testing (JUnit 5 — No Minecraft)

JUnit Platform task

tasks.test {
    useJUnitPlatform()
    testLogging {
        events("passed", "skipped", "failed")
    }
}

For Fabric code that needs loader setup, use Fabric Loader JUnit rather than assuming ordinary JUnit initialized Minecraft:

dependencies {
    testImplementation "net.fabricmc:fabric-loader-junit:${project.loader_version}"
}

test {
    useJUnitPlatform()
}

When a unit test reaches registry-dependent Minecraft classes, initialize only the required bootstrap in test setup. The current Fabric guide uses SharedConstants.tryDetectVersion() and Bootstrap.bootStrap() for that case.

Example pure unit test

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class CooldownManagerTest {

    @Test
    void cooldown_tracksPlayersIndependently() {
        var manager = new CooldownManager(500L); // 500ms cooldown
        manager.startCooldown("steve");
        assertTrue(manager.isOnCooldown("steve"));
        assertFalse(manager.isOnCooldown("notExisting"));
    }

    @Test
    void cooldown_throwsIllegalArgument_onNegativeDuration() {
        assertThrows(IllegalArgumentException.class,
            () -> new CooldownManager(-1L));
    }
}

MockBukkit (Paper/Bukkit Plugin Tests)

build.gradle.kts

repositories {
    maven("https://repo.papermc.io/repository/maven-public/")
    mavenCentral()
}

dependencies {
    compileOnly("io.papermc.paper:paper-api:26.2.build.+")
    testImplementation("org.junit.jupiter:junit-jupiter:6.1.3")
    testImplementation("org.mockbukkit.mockbukkit:mockbukkit-v26.2:4.116.1")
    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
}

tasks.test {
    useJUnitPlatform()
}

Setup / teardown pattern

import org.mockbukkit.mockbukkit.MockBukkit;
import org.mockbukkit.mockbukkit.ServerMock;
import org.mockbukkit.mockbukkit.entity.PlayerMock;
import org.junit.jupiter.api.*;

class MyPluginTest {

    private static ServerMock server;
    private static MyPlugin plugin;

    @BeforeAll
    static void setUp() {
        // Start mock Bukkit server and load your plugin
        server = MockBukkit.mock();
        plugin = MockBukkit.load(MyPlugin.class);
    }

    @AfterAll
    static void tearDown() {
        MockBukkit.unmock();
    }
}

Testing events

@Test
void playerJoin_getsWelcomeMessage() {
    PlayerMock player = server.addPlayer("Steve");
    player.simulateJoin(); // fires PlayerJoinEvent

    // Assert the player received the expected message component
    player.assertSaid("Welcome, Steve!");
    // Or for Adventure components:
    assertTrue(player.nextMessage().contains("Welcome"));
}

@Test
void onBlockBreak_cancelledForNonOp() {
    PlayerMock player = server.addPlayer();
    player.setOp(false);

    Block block = player.getWorld().getBlockAt(0, 64, 0);
    block.setType(Material.STONE);
    BlockBreakEvent event = new BlockBreakEvent(block, player);
    server.getPluginManager().callEvent(event);

    assertTrue(event.isCancelled(), "Non-op should not be able to break blocks");
}

Testing commands

@Test
void mypluginInfo_returnsVersion() {
    PlayerMock player = server.addPlayer("Admin");
    player.setOp(true);

    boolean result = server.dispatchCommand(player, "myplugin info");

    assertTrue(result);
    player.assertSaid("Version: " + plugin.getDescription().getVersion());
}

@Test
void mypluginReload_requiresOp() {
    PlayerMock player = server.addPlayer("NonOp");
    player.setOp(false);

    server.dispatchCommand(player, "myplugin reload");

    player.assertSaid("No permission.");
}

Testing inventory / items

@Test
void giveKitCommand_givesPlayerItems() {
    PlayerMock player = server.addPlayer();
    
    server.dispatchCommand(player, "kit starter");
    
    // Check inventory
    assertTrue(player.getInventory().contains(Material.STONE_SWORD));
    assertTrue(player.getInventory().contains(Material.BREAD, 16));
}

Testing scheduler tasks

@Test
void repeatingTask_firesAfterDelay() {
    PlayerMock player = server.addPlayer();
    
    // Execute 40 ticks worth of scheduled tasks
    server.getScheduler().performTicks(40L);
    
    // Assert expected side effect happened
    assertEquals(2, plugin.getTaskCount());
}

Testing Folia-safe scheduler abstractions

MockBukkit does not emulate Folia's region-threaded runtime. The safe pattern is to wrap scheduling behind your own interface and unit test the abstraction boundary.

interface SchedulerFacade {
    void runPlayerTask(Player player, Runnable task);
    void runAsync(Runnable task);
}

@Test
void playerTask_delegatesThroughFacade() {
    List<String> calls = new ArrayList<>();
    SchedulerFacade facade = new SchedulerFacade() {
        @Override
        public void runPlayerTask(Player player, Runnable task) {
            calls.add("player");
            task.run();
        }

        @Override
        public void runAsync(Runnable task) {
            calls.add("async");
            task.run();
        }
    };

    facade.runPlayerTask(server.addPlayer(), () -> calls.add("ran"));
    assertEquals(List.of("player", "ran"), calls);
}

Testing PDC

import java.util.ArrayList;
import org.bukkit.damage.DamageSource;
import org.bukkit.damage.DamageType;
import org.bukkit.entity.LivingEntity;

@Test
void pdcKillCount_incrementsOnKill() {
    PlayerMock player = server.addPlayer();
    NamespacedKey key = new NamespacedKey(plugin, "kills");

    // EntityDeathEvent requires a living victim and an explicit damage source.
    LivingEntity victim = (LivingEntity) server.addMockEntity(EntityType.ZOMBIE);
    DamageSource damageSource = DamageSource.builder(DamageType.GENERIC)
        .withCausingEntity(player)
        .withDirectEntity(player)
        .build();
    EntityDeathEvent deathEvent = new EntityDeathEvent(
        victim, damageSource, new ArrayList<>(), 0
    );
    server.getPluginManager().callEvent(deathEvent);

    int kills = player.getPersistentDataContainer()
        .getOrDefault(key, PersistentDataType.INTEGER, 0);
    assertEquals(1, kills);
}

This dispatches a synthetic death event. For player attribution, the listener under test should read event.getDamageSource().getCausingEntity(); test actual combat attribution separately on a real server.

Testing item or chunk PDC writes

@Test
void itemPdc_roundTripsCustomId() {
    NamespacedKey key = new NamespacedKey(plugin, "custom_id");
    ItemStack item = new ItemStack(Material.STICK);

    item.editMeta(meta -> meta.getPersistentDataContainer().set(
        key, PersistentDataType.STRING, "wand"
    ));

    String value = item.getItemMeta().getPersistentDataContainer()
        .get(key, PersistentDataType.STRING);
    assertEquals("wand", value);
}

Current NeoForge Game Tests (26.x)

NeoForge 1.21.5 and later uses data-driven test environments and test instances, not the old @GameTestHolder method-registration API. Store resources under data/<namespace>/test_environment/ and data/<namespace>/test_instance/. A test_instance selects its environment, structure, timing, and either a registered function or a block-based test.

{
  "environment": "minecraft:default",
  "structure": "examplemod:example_structure",
  "max_ticks": 200,
  "setup_ticks": 0,
  "required": true,
  "type": "minecraft:function",
  "function": "examplemod:example_function"
}

Register the Consumer<GameTestHelper> with a DeferredRegister for the current BuiltInRegistries.TEST_FUNCTION registry, then attach that register to the mod event bus. The function below makes the JSON reference above usable. Use RegisterGameTestsEvent only when registering environments and test instances in code instead of data files. Keep the referenced structure in data/<namespace>/structure/<path>.nbt and mark success explicitly.

import java.util.function.Consumer;
import net.minecraft.core.registries.BuiltInRegistries;
import net.minecraft.gametest.framework.GameTestHelper;
import net.minecraft.world.level.block.Blocks;
import net.neoforged.bus.api.IEventBus;
import net.neoforged.fml.common.Mod;
import net.neoforged.neoforge.registries.DeferredHolder;
import net.neoforged.neoforge.registries.DeferredRegister;

@Mod(ExampleGameTests.MOD_ID)
public final class ExampleGameTests {
    public static final String MOD_ID = "examplemod";
    private static final DeferredRegister<Consumer<GameTestHelper>> TEST_FUNCTIONS =
        DeferredRegister.create(BuiltInRegistries.TEST_FUNCTION, MOD_ID);
    public static final DeferredHolder<Consumer<GameTestHelper>, Consumer<GameTestHelper>>
        EXAMPLE_FUNCTION = TEST_FUNCTIONS.register(
            "example_function", () -> ExampleGameTests::exampleTest
        );

    public ExampleGameTests(IEventBus modBus) {
        TEST_FUNCTIONS.register(modBus);
    }

    public static void exampleTest(GameTestHelper helper) {
        helper.assertBlockPresent(Blocks.AIR, 0, 0, 0);
        helper.succeed();
    }
}

Run ./gradlew runGameTestServer; the server exits with the count of required failed tests. This command is for a real project, not this skills repository.

Current Fabric Game Tests (26.x)

Use Fabric Loom's dedicated Game Test source set. Configure it in the existing fabricApi block and keep its metadata and code under src/gametest, separate from ordinary unit tests.

fabricApi {
    configureTests {
        createSourceSet = true
        modId = "example-mod-test-${project.name}"
        enableGameTests = true
        enableClientGameTests = true
        eula = true
    }
}

Place fabric.mod.json in src/gametest/resources/ and register server tests under fabric-gametest; use fabric-client-gametest for client tests. Implement server methods with Fabric's net.fabricmc.fabric.api.gametest.v1.GameTest and, when setup is needed before a method runs, CustomTestMethodInvoker.

package com.example.mymod;

import java.lang.reflect.Method;
import net.fabricmc.fabric.api.gametest.v1.CustomTestMethodInvoker;
import net.fabricmc.fabric.api.gametest.v1.GameTest;
import net.minecraft.gametest.framework.GameTestHelper;
import net.minecraft.world.level.block.Blocks;

public final class ExampleGameTest implements CustomTestMethodInvoker {
    @GameTest
    public void testBlock(GameTestHelper context) {
        context.assertBlockPresent(Blocks.AIR, 0, 0, 0);
        context.succeed();
    }

    @Override
    public void invokeTestMethod(GameTestHelper context, Method method)
            throws ReflectiveOperationException {
        method.invoke(this, context);
    }
}

src/gametest/resources/fabric.mod.json

{
  "entrypoints": {
    "fabric-gametest": [
      "com.example.mymod.ExampleGameTest"
    ]
  }
}

Keep the fabric-gametest entrypoint in sync with the concrete Game Test class. Fabric's server Game Tests run with build; use runClientGameTest for client tests. Follow the current Fabric documentation for project-specific Loom options and headless client CI.

Legacy NeoForge Game Tests (1.21.3 only)

Keep annotation-based tests isolated to an explicit 1.21.3 lane. The class can be registered by either @GameTestHolder(MOD_ID) or a RegisterGameTestsEvent listener. Do not register a @GameTestHolder class again with modEventBus.register(MyGameTests.class).

import net.minecraft.gametest.framework.GameTest;
import net.minecraft.gametest.framework.GameTestHelper;
import net.neoforged.neoforge.gametest.GameTestHolder;
import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;

@GameTestHolder("examplemod")
@PrefixGameTestTemplate(false)
public final class ExampleGameTests {
    @GameTest(template = "example_structure")
    public static void smoke(GameTestHelper helper) {
        helper.succeed();
    }
}

For RegisterGameTestsEvent, register the class on the mod event bus and set templateNamespace = MOD_ID on each @GameTest. Legacy templates are .nbt files under data/<namespace>/structure/; @PrefixGameTestTemplate(false) controls whether the class name is added to the template path. When template is omitted, the path uses the lowercase method name and, unless that prefix is disabled, the lowercase simple class name followed by a dot. template is the path name only; configure its namespace through templateNamespace or @GameTestHolder.

CI

Keep fast unit/mock tests separate from a loader's Game Test task, and select the Java version by lane: 25 for 26.x, 21 for 1.21.x, and 17 for Forge 1.20.1. Upload test reports when a runtime-facing job fails. Do not assume a task name from another loader: Fabric server Game Tests run with build, while NeoForge uses runGameTestServer. MockBukkit does not prove Folia thread safety or real server bootstrap.

References

• MockBukkit GitHub: https://github.com/MockBukkit/MockBukkit
• MockBukkit docs: https://docs.mockbukkit.org/
• Fabric automated testing: https://docs.fabricmc.net/develop/automatic-testing
• NeoForge 26.x Game Tests: https://docs.neoforged.net/docs/misc/gametest/
• NeoForge 1.21.3 Game Tests: https://docs.neoforged.net/docs/1.21.3/misc/gametest/
• JUnit 5 user guide: https://junit.org/junit5/docs/current/user-guide/