app/build.gradle

@@ -27,7 +27,7 @@ dependencies {
 
 application {
     // Define the main class for the application.
-    mainClass = 'school_project.App'
+    mainClass = 'school_project.Controller'
 }
 
 javafx {

app/src/main/java/school_project/App.java

@@ -1,14 +0,0 @@
-/*
- * This Java source file was generated by the Gradle 'init' task.
- */
-package school_project;
-
-public class App {
-    public String getGreeting() {
-        return "Hello World!";
-    }
-
-    public static void main(String[] args) {
-        System.out.println(new App().getGreeting());
-    }
-}

app/src/main/java/school_project/Controller.java

@@ -0,0 +1,32 @@
+/*
+ * This Java source file was generated by the Gradle 'init' task.
+ */
+package school_project;
+
+import javafx.application.Application;
+import javafx.scene.Group;
+import javafx.scene.Scene;
+import javafx.scene.control.Button;
+import javafx.stage.Stage;
+
+public class Controller extends Application {
+
+    @Override
+    public void start(Stage primaryStage) throws Exception {
+        primaryStage.setTitle("test");
+        Button btn = new Button("test");
+        btn.setOnAction(event -> System.out.println("hey"));
+
+        Group root = new Group();
+        root.getChildren().add(btn);
+
+        Scene scene = new Scene(root, 300,300);
+        primaryStage.setScene(scene);
+
+        primaryStage.show();
+    }
+
+    public static void main(String[] args) {
+       launch();
+    }
+}

app/src/test/java/school_project/AppTest.java

@@ -4,11 +4,9 @@
 package school_project;
 
 import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.*;
 
 class AppTest {
     @Test void appHasAGreeting() {
-        App classUnderTest = new App();
-        assertNotNull(classUnderTest.getGreeting(), "app should have a greeting");
+        Controller classUnderTest = new Controller();
     }
 }