How to write unit testing checking null input values using wicket

Question

I am busy with a wicket application and need to do unit testing, and I have a login page that validates inputs from a List<Customer> but I have no idea where to start, I did try something but it gave me errors and just have no clue what I am doing any help is appreciated

Homepage.java

     form.add(new AjaxButton("error") {

            private static final long serialVersionUID = 1L;

            @Override
            protected void onSubmit(AjaxRequestTarget target)
            {
                for (Customer item: lstCustomer){

                    if (item.name.equals(username.getInput()) && item.password.equals(password.getInput())){

                        final String usernameValue = username.getModelObject();

                        PageParameters pp = new PageParameters();
                        pp.add("username", usernameValue);
                        setResponsePage(SuccessPage.class, pp);
                        valid[0] = true;
                        break;

                    }else {
                        logger.error("In the else");
                        valid[0] = false ;
                    }
                }

                if ( valid[0] == false){

                    errorDialog.open(target);

                }


            }
        });

TestPage

private WicketTester tester;

    @Before
    public void setUp()
    {
        tester = new WicketTester(new WicketApplication());
    }

    @Test
    public void homepageRendersSuccessfully()
    {
        //start and render the test page
        tester.startPage(HomePage.class);

        //assert rendered page class
        tester.assertRenderedPage(HomePage.class);


    }

    @Test
    public void validLogin(){
        FormTester form = tester.newFormTester("userForm");
        form.setValue("username", "emile");
        form.setValue("password", "123");
        form.submit();
        tester.assertRenderedPage(SuccessPage.class);

    }

And then I get this error :

[main] INFO org.apache.wicket.Application - [WicketTesterApplication-b020ca32-fe17-43e9-8cc5-3b7a618b2f93] init: Wicket extensions initializer
[main] INFO org.apache.wicket.Application - [WicketTesterApplication-b020ca32-fe17-43e9-8cc5-3b7a618b2f93] init: Wicket jQuery UI initializer
[main] INFO org.apache.wicket.Application - [WicketTesterApplication-b020ca32-fe17-43e9-8cc5-3b7a618b2f93] init: Wicket jQuery UI initializer (theme-uilightness)

java.lang.NullPointerException
    at org.apache.wicket.util.tester.BaseWicketTester.getComponentFromLastRenderedPage(BaseWicketTester.java:1593)
    at org.apache.wicket.util.tester.BaseWicketTester.getComponentFromLastRenderedPage(BaseWicketTester.java:1516)
    at org.apache.wicket.util.tester.BaseWicketTester.getComponentFromLastRenderedPage(BaseWicketTester.java:1625)
    at org.apache.wicket.util.tester.BaseWicketTester.newFormTester(BaseWicketTester.java:1311)
    at org.apache.wicket.util.tester.BaseWicketTester.newFormTester(BaseWicketTester.java:1295)
    at com.mycompany.TestHomePage.validLogin(TestHomePage.java:35)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)

Answer 1

you must set a starting page in validLogin() before creating a formTester:

@Test
public void validLogin(){
    //here...
    tester.startPage(HomePage.class);

    FormTester form = tester.newFormTester("userForm");
    form.setValue("username", "emile");
    form.setValue("password", "123");
    form.submit();
    tester.assertRenderedPage(SuccessPage.class);

}