Getting NullPointerException in JUNit testing

Question

I am trying to do some JUnit testing for a college assignment but I get an error every time I try to run my tests. When I first created my file it worked fine but after I restarted my Intellij this started happening for some unknown reason. I have created this file to test input for the number of players entered. The test should fail if the value is below 2 or above 4. Even after removing the failed test cases I get the error. I have tried reinstalling java and javafx but the issue still remains. I've tried in vscode and intellij but no luck so far. This is the error:

java.lang.NullPointerException: Cannot invoke "com.sun.glass.ui.Timer.resume()" because "this.pulseTimer" is null

    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.QuantumToolkit.resumeTimer(QuantumToolkit.java:525)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.QuantumToolkit$PulseTask.set(QuantumToolkit.java:213)
    at javafx.graphics@19-ea/com.sun.javafx.tk.quantum.QuantumToolkit.requestNextPulse(QuantumToolkit.java:887)
    at javafx.graphics@19-ea/javafx.scene.Parent.markDirtyLayout(Parent.java:939)
    at javafx.graphics@19-ea/javafx.scene.Parent.requestLayout(Parent.java:963)
    at javafx.graphics@19-ea/javafx.scene.Scene$8.invalidated(Scene.java:1231)
    at javafx.base@19-ea/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
    at javafx.base@19-ea/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
    at javafx.graphics@19-ea/javafx.scene.Scene.setRoot(Scene.java:1181)
    at javafx.graphics@19-ea/javafx.scene.Scene.<init>(Scene.java:359)
    at javafx.graphics@19-ea/javafx.scene.Scene.<init>(Scene.java:239)
    at com.cascadia.demo@1.0-SNAPSHOT/com.cascadia.demo.ViewLauncher.<init>(ViewLauncher.java:47)
    at com.cascadia.demo@1.0-SNAPSHOT/com.cascadia.demo.ViewLauncherTest.testGetNumPlayer(ViewLauncherTest.java:18)
    at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
    at java.base/java.lang.reflect.Method.invoke(Method.java:578)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:107)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:114)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:86)
    at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:86)
    at org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:53)
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:57)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
    at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)

The JUnit code is:


import javafx.scene.control.TextField;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class ViewLauncherTest {

    @Test
    public void testSetNumPlayer() {
        ViewLauncher view = new ViewLauncher();
        view.setNum_Player(new TextField("3"));
        Assertions.assertEquals(3, view.getNum_Player());
    }

    @Test
    public void testGetNumPlayer() {
        ViewLauncher view = new ViewLauncher();
        view.setNum_Player(new TextField("4"));
        Assertions.assertEquals(4, view.getNum_Player());
    }

    @Test
    public void testInvalidNumPlayer() {
        ViewLauncher view = new ViewLauncher();
        view.setNum_Player(new TextField("5"));
        Assertions.assertThrows(NumberFormatException.class, () -> view.getNum_Player());
    }

}

Follow [java naming conventions](https://www.oracle.com/java/technologies/javase/codeconventions-namingconventions.html). Don't use `ea` (early access) software versions, unless you need early access functionality (highly unlikely). — jewelsea, Apr 02 '23 at 08:25

jewelsea · Answer 1 · 2023-04-04T19:15:42.480

The null pointer exception is not in your code. Neither is there an error in the code which throws the exception.

The issue is in how you are using the API. You can't use most JavaFX APIs without starting up the JavaFX platform on which the API implementations rely. You haven't done that in your tests that I can see. The Application javadoc explains the JavaFX lifecycle and how it is used.

What is needed is to startup the JavaFX platform, run a test (or tests) then exit the platform after all tests have been run.

If you want to use junit to test code that uses JavaFX, IMO it is best to use a 3rd party framework that supports that (e.g. TestFX). I advise this over trying to manually manage the JavaFX platform state in the code that you write.

Alternately, you can separate out much of your code logic from JavaFX code (this is a good idea in any case), and test the non-JavaFX logic independently using standard testing tools like junit, then test the UI elements manually.

Your tests and API design are strange. You have:

view.setNum_Player(new TextField("4"));
Assertions.assertEquals(4, view.getNum_Player());

You set the number of players to a TextField, but when you get the number of players, you expect an integer. That doesn't make a lot of sense. If you get and set a value on a bean, it should get and set the same value and type by convention. In your case, it should be an integer, not a TextField.

Getting NullPointerException in JUNit testing

1 Answers1