Added two stubs for tests

build.gradle

@@ -65,6 +65,8 @@ dependencies {
     testImplementation(enforcedPlatform("org.junit:junit-bom:5.10.2"))
     testImplementation 'org.junit.jupiter:junit-jupiter-api'
     testImplementation 'org.junit.jupiter:junit-jupiter-params'
+    testImplementation 'org.assertj:assertj-core:3.25.1'
+    testImplementation gradleTestKit()
     testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine'
     testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
 }
@@ -119,3 +121,9 @@ gradlePlugin {
 test {
     useJUnitPlatform()
 }
+
+// The java-gradle-plugin ignores the java8 source-set we added to the main source sets classpath
+// For testkit tests to work, this needs to be present
+tasks.withType(PluginUnderTestMetadata).configureEach {
+    it.pluginClasspath.from(sourceSets.java8.output.classesDirs)
+}

src/main/java/net/neoforged/moddevgradle/internal/ModDevPlugin.java

@@ -57,6 +57,8 @@ public class ModDevPlugin implements Plugin<Project> {
 
     private static final String JAR_JAR_GROUP = "jarjar";
 
+    private static final String TASK_GROUP = "mod development";
+
     @Override
     public void apply(Project project) {
         project.getPlugins().apply(JavaLibraryPlugin.class);
@@ -344,7 +346,7 @@ public void apply(Project project) {
             idePostSyncTask.configure(task -> task.dependsOn(prepareRunTask));
 
             tasks.register(InternalModelHelper.nameOfRun(run, "run", ""), RunGameTask.class, task -> {
-                task.setGroup("neoforge moddev");
+                task.setGroup(TASK_GROUP);
 
                 // Launch with the Java version used in the project
                 var toolchainService = ExtensionUtils.findExtension(project, "javaToolchains", JavaToolchainService.class);

src/test/java/net/neoforged/moddevgradle/functional/GroovyScriptTest.java

@@ -0,0 +1,63 @@
+package net.neoforged.moddevgradle.functional;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.gradle.testkit.runner.GradleRunner;
+import org.gradle.testkit.runner.TaskOutcome;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class GroovyScriptTest {
+    @TempDir
+    File testProjectDir;
+    private File settingsFile;
+    private File buildFile;
+
+    @BeforeEach
+    public void setup() {
+        settingsFile = new File(testProjectDir, "settings.gradle");
+        buildFile = new File(testProjectDir, "build.gradle");
+    }
+
+    @Test
+    public void testApplyInEmptyProject() throws IOException {
+        writeFile(settingsFile, "rootProject.name = 'hello-world'");
+        String buildFileContent = """
+                plugins {
+                    id "net.neoforged.moddev"
+                }
+                """;
+        writeFile(buildFile, buildFileContent);
+
+        BuildResult result = GradleRunner.create()
+                .withPluginClasspath()
+                .withProjectDir(testProjectDir)
+                .withArguments("tasks", "--all")
+                .build();
+
+        assertThat(result.getOutput()).contains("createMinecraftArtifacts");
+        assertEquals(TaskOutcome.SUCCESS, result.task(":tasks").getOutcome());
+    }
+
+    private void writeFile(File destination, String content) throws IOException {
+        BufferedWriter output = null;
+        try {
+            output = new BufferedWriter(new FileWriter(destination));
+            output.write(content);
+        } finally {
+            if (output != null) {
+                output.close();
+            }
+        }
+
+
+    }
+}

src/test/java/net/neoforged/moddevgradle/functional/KotlinScriptTest.java

@@ -0,0 +1,65 @@
+package net.neoforged.moddevgradle.functional;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.gradle.testkit.runner.GradleRunner;
+import org.gradle.testkit.runner.TaskOutcome;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class KotlinScriptTest {
+    @TempDir
+    File testProjectDir;
+    private File settingsFile;
+    private File buildFile;
+
+    @BeforeEach
+    public void setup() {
+        settingsFile = new File(testProjectDir, "settings.gradle.kts");
+        buildFile = new File(testProjectDir, "build.gradle.kts");
+    }
+
+    @Test
+    public void testApplyInEmptyProject() throws IOException {
+        writeFile(settingsFile, """
+                rootProject.name = "hello-world";
+                """);
+        String buildFileContent = """
+                plugins {
+                    id("net.neoforged.moddev")
+                }
+                """;
+        writeFile(buildFile, buildFileContent);
+
+        BuildResult result = GradleRunner.create()
+                .withPluginClasspath()
+                .withProjectDir(testProjectDir)
+                .withArguments("tasks", "--all")
+                .build();
+
+        assertThat(result.getOutput()).contains("createMinecraftArtifacts");
+        assertEquals(TaskOutcome.SUCCESS, result.task(":tasks").getOutcome());
+    }
+
+    private void writeFile(File destination, String content) throws IOException {
+        BufferedWriter output = null;
+        try {
+            output = new BufferedWriter(new FileWriter(destination));
+            output.write(content);
+        } finally {
+            if (output != null) {
+                output.close();
+            }
+        }
+
+
+    }
+}